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Javascript convert PascalCase to underscore_case/snake_case

How can I convert PascalCase string into underscore_case/snake_case string? I need to convert dots into underscores as well.
eg. convert
TypeOfData.AlphaBeta
into
type_of_data_alpha_beta

You could try the below steps.
Capture all the uppercase letters and also match the preceding optional dot character.
Then convert the captured uppercase letters to lowercase and then return back to replace function with an _ as preceding character. This will be achieved by using anonymous function in the replacement part.
This would replace the starting uppercase letter to _ + lowercase_letter.
Finally removing the starting underscore will give you the desired output.
var s = 'TypeOfData.AlphaBeta';
console.log(s.replace(/(?:^|\.?)([A-Z])/g, function (x,y){return "_" + y.toLowerCase()}).replace(/^_/, ""));
OR
var s = 'TypeOfData.AlphaBeta';
alert(s.replace(/\.?([A-Z])/g, function (x,y){return "_" + y.toLowerCase()}).replace(/^_/, ""));
any way to stop it for when a whole word is in uppercase. eg. MotorRPM into motor_rpm instead of motor_r_p_m? or BatteryAAA into battery_aaa instead of battery_a_a_a?
var s = 'MotorRMP';
alert(s.replace(/\.?([A-Z]+)/g, function (x,y){return "_" + y.toLowerCase()}).replace(/^_/, ""));

str.split(/\.?(?=[A-Z])/).join('_').toLowerCase();
u're welcome
var s1 = 'someTextHere';
var s2 = 'SomeTextHere';
var s3 = 'TypeOfData.AlphaBeta';
var o1 = s1.split(/\.?(?=[A-Z])/).join('_').toLowerCase();
var o2 = s2.split(/\.?(?=[A-Z])/).join('_').toLowerCase();
var o3 = s3.split(/\.?(?=[A-Z])/).join('_').toLowerCase();
console.log(o1);
console.log(o2);
console.log(o3);

Alternatively using lodash:
lodash.snakeCase(str);
Example:
_.snakeCase('TypeOfData.AlphaBeta');
// ➜ 'type_of_data_alpha_beta'
Lodash is a fine library to give shortcut to many everyday js tasks.There are many other similar string manipulation functions such as camelCase, kebabCase etc.

This solution solves the non-trailing acronym issue with the solutions above
I ported the code in 1175208 from Python to JavaScript.
Javascript Code
function camelToSnakeCase(text) {
return text.replace(/(.)([A-Z][a-z]+)/, '$1_$2').replace(/([a-z0-9])([A-Z])/, '$1_$2').toLowerCase()
}
Working Examples:
camelToSnakeCase('thisISDifficult') -> this_is_difficult
camelToSnakeCase('thisISNT') -> this_isnt
camelToSnakeCase('somethingEasyLikeThis') -> something_easy_like_this

"alphaBetaGama".replace(/([A-Z])/g, "_$1").toLowerCase() // alpha_beta_gamma
Problem - Need to convert a camel-case string ( such as a property name ) into underscore style to meet interface requirements or for meta-programming.
Explanation
This line uses a feature of regular expressions where it can return a matched result ( first pair of () is $1, second is $2, etc ).
Each match in the string is converted to have an underscore ahead of it with _$1 string provided. At that point the string looks like alpha_Beta_Gamma.
To correct the capitalization, the entire string is converted toLowerCase().
Since toLowerCase is a fairly expensive operation, its best not to put it in the looping handler for each match-case, and run it once on the entire string.
After toLowerCase it the resulting string is alpha_beta_gamma ( in this example )

This will get you pretty far: https://github.com/domchristie/humps
You will probably have to use regex replace to replace the "." with an underscore.

I found this but I edited it so suit your question.
const camelToSnakeCase = str => str.replace(/[A-Z]/g, letter => `_${letter.toLowerCase()}`).replace(/^_/,'')

Good examples for js:
Snake Case
Kebab Case
Camel Case
Pascal Case
have here

function toCamelCase(s) {
// remove all characters that should not be in a variable name
// as well underscores an numbers from the beginning of the string
s = s.replace(/([^a-zA-Z0-9_\- ])|^[_0-9]+/g, "").trim().toLowerCase();
// uppercase letters preceeded by a hyphen or a space
s = s.replace(/([ -]+)([a-zA-Z0-9])/g, function(a,b,c) {
return c.toUpperCase();
});
// uppercase letters following numbers
s = s.replace(/([0-9]+)([a-zA-Z])/g, function(a,b,c) {
return b + c.toUpperCase();
});
return s;
}
Try this function, hope it helps.

"TestString".replace(/[A-Z]/g, val => "_" + val.toLowerCase()).replace(/^_/,"")
replaces all uppercase with an underscore and lowercase, then removes the leading underscore.

A Non-Regex Answer that converts PascalCase to snake_case
Note: I understand there are tons of good answers which solve this question elegantly. I was recently working on something similar to this where I chose not to use regex. So I felt to answer a non-regex solution to this.
const toSnakeCase = (str) => {
return str.slice(0,1).toLowerCase() + str.split('').slice(1).map((char) => {
if (char == char.toUpperCase()) return '_' + char.toLowerCase();
else return char;
}).join('');
}
Eg.
inputString = "ILoveJavascript" passed onto toSnakeCase()
would become "i_love_javascript"

How to use Javascript to change link [duplicate]

I've got a data-123 string.
How can I remove data- from the string while leaving the 123?

var ret = "data-123".replace('data-','');
console.log(ret); //prints: 123
Docs.
For all occurrences to be discarded use:
var ret = "data-123".replace(/data-/g,'');
PS: The replace function returns a new string and leaves the original string unchanged, so use the function return value after the replace() call.

This doesn't have anything to do with jQuery. You can use the JavaScript replace function for this:
var str = "data-123";
str = str.replace("data-", "");
You can also pass a regex to this function. In the following example, it would replace everything except numerics:
str = str.replace(/[^0-9\.]+/g, "");

You can use "data-123".replace('data-','');, as mentioned, but as replace() only replaces the FIRST instance of the matching text, if your string was something like "data-123data-" then
"data-123data-".replace('data-','');
will only replace the first matching text. And your output will be "123data-"
DEMO
So if you want all matches of text to be replaced in string you have to use a regular expression with the g flag like that:
"data-123data-".replace(/data-/g,'');
And your output will be "123"
DEMO2

You can use slice(), if you will know in advance how many characters need slicing off the original string. It returns characters between a given start point to an end point.
string.slice(start, end);
Here are some examples showing how it works:
var mystr = ("data-123").slice(5); // This just defines a start point so the output is "123"
var mystr = ("data-123").slice(5,7); // This defines a start and an end so the output is "12"
Demo

Plain old JavaScript will suffice - jQuery is not necessary for such a simple task:
var myString = "data-123";
var myNewString = myString.replace("data-", "");
See: .replace() docs on MDN for additional information and usage.

1- If is the sequences into your string:
let myString = "mytest-text";
let myNewString = myString.replace("mytest-", "");
the answer is text
2- if you whant to remove the first 3 characters:
"mytest-text".substring(3);
the answer is est-text

Ex:-
var value="Data-123";
var removeData=value.replace("Data-","");
alert(removeData);
Hopefully this will work for you.

Performance
Today 2021.01.14 I perform tests on MacOs HighSierra 10.13.6 on Chrome v87, Safari v13.1.2 and Firefox v84 for chosen solutions.
Results
For all browsers
solutions Ba, Cb, and Db are fast/fastest for long strings
solutions Ca, Da are fast/fastest for short strings
solutions Ab and E are slow for long strings
solutions Ba, Bb and F are slow for short strings
Details
I perform 2 tests cases:
short string - 10 chars - you can run it HERE
long string - 1 000 000 chars - you can run it HERE
Below snippet presents solutions
Aa
Ab
Ba
Bb
Ca
Cb
Da
Db
E
F
// https://stackoverflow.com/questions/10398931/how-to-strToRemove-text-from-a-string
// https://stackoverflow.com/a/10398941/860099
function Aa(str,strToRemove) {
return str.replace(strToRemove,'');
}
// https://stackoverflow.com/a/63362111/860099
function Ab(str,strToRemove) {
return str.replaceAll(strToRemove,'');
}
// https://stackoverflow.com/a/23539019/860099
function Ba(str,strToRemove) {
let re = strToRemove.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); // regexp escape char
return str.replace(new RegExp(re),'');
}
// https://stackoverflow.com/a/63362111/860099
function Bb(str,strToRemove) {
let re = strToRemove.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); // regexp escape char
return str.replaceAll(new RegExp(re,'g'),'');
}
// https://stackoverflow.com/a/27098801/860099
function Ca(str,strToRemove) {
let start = str.indexOf(strToRemove);
return str.slice(0,start) + str.slice(start+strToRemove.length, str.length);
}
// https://stackoverflow.com/a/27098801/860099
function Cb(str,strToRemove) {
let start = str.search(strToRemove);
return str.slice(0,start) + str.slice(start+strToRemove.length, str.length);
}
// https://stackoverflow.com/a/23181792/860099
function Da(str,strToRemove) {
let start = str.indexOf(strToRemove);
return str.substr(0, start) + str.substr(start + strToRemove.length);
}
// https://stackoverflow.com/a/23181792/860099
function Db(str,strToRemove) {
let start = str.search(strToRemove);
return str.substr(0, start) + str.substr(start + strToRemove.length);
}
// https://stackoverflow.com/a/49857431/860099
function E(str,strToRemove) {
return str.split(strToRemove).join('');
}
// https://stackoverflow.com/a/45406624/860099
function F(str,strToRemove) {
var n = str.search(strToRemove);
while (str.search(strToRemove) > -1) {
n = str.search(strToRemove);
str = str.substring(0, n) + str.substring(n + strToRemove.length, str.length);
}
return str;
}
let str = "data-123";
let strToRemove = "data-";
[Aa,Ab,Ba,Bb,Ca,Cb,Da,Db,E,F].map( f=> console.log(`${f.name.padEnd(2,' ')} ${f(str,strToRemove)}`));
This shippet only presents functions used in performance tests - it not perform tests itself!
And here are example results for chrome

This little function I made has always worked for me :)
String.prototype.deleteWord = function (searchTerm) {
var str = this;
var n = str.search(searchTerm);
while (str.search(searchTerm) > -1) {
n = str.search(searchTerm);
str = str.substring(0, n) + str.substring(n + searchTerm.length, str.length);
}
return str;
}
// Use it like this:
var string = "text is the cool!!";
string.deleteWord('the'); // Returns text is cool!!
I know it is not the best, but It has always worked for me :)

str.split('Yes').join('No');
This will replace all the occurrences of that specific string from original string.

I was used to the C# (Sharp) String.Remove method.
In Javascript, there is no remove function for string, but there is substr function.
You can use the substr function once or twice to remove characters from string.
You can make the following function to remove characters at start index to the end of string, just like the c# method first overload String.Remove(int startIndex):
function Remove(str, startIndex) {
return str.substr(0, startIndex);
}
and/or you also can make the following function to remove characters at start index and count, just like the c# method second overload String.Remove(int startIndex, int count):
function Remove(str, startIndex, count) {
return str.substr(0, startIndex) + str.substr(startIndex + count);
}
and then you can use these two functions or one of them for your needs!
Example:
alert(Remove("data-123", 0, 5));
Output: 123

Using match() and Number() to return a number variable:
Number(("data-123").match(/\d+$/));
// strNum = 123
Here's what the statement above does...working middle-out:
str.match(/\d+$/) - returns an array containing matches to any length of numbers at the end of str. In this case it returns an array containing a single string item ['123'].
Number() - converts it to a number type. Because the array returned from .match() contains a single element Number() will return the number.

Update 2023
There are many ways to solve this problem, but I believe this is the simplest:
const newString = string.split("data-").pop();
console.log(newString); /// 123

For doing such a thing there are a lot of different ways. A further way could be the following:
let str = 'data-123';
str = str.split('-')[1];
console.log('The remaining string is:\n' + str);
Basically the above code splits the string at the '-' char into two array elements and gets the second one, that is the one with the index 1, ignoring the first array element at the 0 index.
The following is one liner version:
console.log('The remaining string is:\n' + 'data-123'.split('-')[1]);
Another possible approach would be to add a method to the String prototype as follows:
String.prototype.remove = function (s){return this.replace(s,'')}
// After that it will be used like this:
a = 'ktkhkiksk kiksk ktkhkek kcklkekaknk kmkekskskakgkekk';
a = a.remove('k');
console.log(a);
Notice the above snippet will allow to remove only the first instance of the string you are interested to remove. But you can improve it a bit as follows:
String.prototype.removeAll = function (s){return this.replaceAll(s,'')}
// After that it will be used like this:
a = 'ktkhkiksk kiksk ktkhkek kcklkekaknk kmkekskskakgkekk';
a = a.removeAll('k');
console.log(a);
The above snippet instead will remove all instances of the string passed to the method.
Of course you don't need to implement the functions into the prototype of the String object: you can implement them as simple functions too if you wish (I will show the remove all function, for the other you will need to use just replace instead of replaceAll, so it is trivial to implement):
function strRemoveAll(s,r)
{
return s.replaceAll(r,'');
}
// you can use it as:
let a = 'ktkhkiksk kiksk ktkhkek kcklkekaknk kmkekskskakgkekk'
b = strRemoveAll (a,'k');
console.log(b);
Of course much more is possible.

Another way to replace all instances of a string is to use the new (as of August 2020) String.prototype.replaceAll() method.
It accepts either a string or RegEx as its first argument, and replaces all matches found with its second parameter, either a string or a function to generate the string.
As far as support goes, at time of writing, this method has adoption in current versions of all major desktop browsers* (even Opera!), except IE. For mobile, iOS SafariiOS 13.7+, Android Chromev85+, and Android Firefoxv79+ are all supported as well.
* This includes Edge/ Chrome v85+, Firefox v77+, Safari 13.1+, and Opera v71+
It'll take time for users to update to supported browser versions, but now that there's wide browser support, time is the only obstacle.
References:
MDN
Can I Use - Current Browser Support Information
TC39 Proposal Repo for .replaceAll()
You can test your current browser in the snippet below:
//Example coutesy of MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replaceAll
const p = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?';
const regex = /dog/gi;
try {
console.log(p.replaceAll(regex, 'ferret'));
// expected output: "The quick brown fox jumps over the lazy ferret. If the ferret reacted, was it really lazy?"
console.log(p.replaceAll('dog', 'monkey'));
// expected output: "The quick brown fox jumps over the lazy monkey. If the monkey reacted, was it really lazy?"
console.log('Your browser is supported!');
} catch (e) {
console.log('Your browser is unsupported! :(');
}
.as-console-wrapper: {
max-height: 100% !important;
}

Make sure that if you are replacing strings in a loop that you initiate a new Regex in each iteration. As of 9/21/21, this is still a known issue with Regex essentially missing every other match. This threw me for a loop when I encountered this the first time:
yourArray.forEach((string) => {
string.replace(new RegExp(__your_regex__), '___desired_replacement_value___');
})
If you try and do it like so, don't be surprised if only every other one works
let reg = new RegExp('your regex');
yourArray.forEach((string) => {
string.replace(reg, '___desired_replacement_value___');
})

trim certain number of characters from end of javascript string [duplicate]

I have a string, 12345.00, and I would like it to return 12345.0.
I have looked at trim, but it looks like it is only trimming whitespace and slice which I don't see how this would work. Any suggestions?

You can use the substring function:
let str = "12345.00";
str = str.substring(0, str.length - 1);
console.log(str);
This is the accepted answer, but as per the conversations below, the slice syntax is much clearer:
let str = "12345.00";
str = str.slice(0, -1);
console.log(str);

You can use slice! You just have to make sure you know how to use it. Positive #s are relative to the beginning, negative numbers are relative to the end.
js>"12345.00".slice(0,-1)
12345.0

You can use the substring method of JavaScript string objects:
s = s.substring(0, s.length - 4)
It unconditionally removes the last four characters from string s.
However, if you want to conditionally remove the last four characters, only if they are exactly _bar:
var re = /_bar$/;
s.replace(re, "");

The easiest method is to use the slice method of the string, which allows negative positions (corresponding to offsets from the end of the string):
const s = "your string";
const withoutLastFourChars = s.slice(0, -4);
If you needed something more general to remove everything after (and including) the last underscore, you could do the following (so long as s is guaranteed to contain at least one underscore):
const s = "your_string";
const withoutLastChunk = s.slice(0, s.lastIndexOf("_"));
console.log(withoutLastChunk);

For a number like your example, I would recommend doing this over substring:
console.log(parseFloat('12345.00').toFixed(1));
Do note that this will actually round the number, though, which I would imagine is desired but maybe not:
console.log(parseFloat('12345.46').toFixed(1));

Be aware that String.prototype.{ split, slice, substr, substring } operate on UTF-16 encoded strings
None of the previous answers are Unicode-aware.
Strings are encoded as UTF-16 in most modern JavaScript engines, but higher Unicode code points require surrogate pairs, so older, pre-existing string methods operate on UTF-16 code units, not Unicode code points.
See: Do NOT use .split('').
const string = "ẞ🦊";
console.log(string.slice(0, -1)); // "ẞ\ud83e"
console.log(string.substr(0, string.length - 1)); // "ẞ\ud83e"
console.log(string.substring(0, string.length - 1)); // "ẞ\ud83e"
console.log(string.replace(/.$/, "")); // "ẞ\ud83e"
console.log(string.match(/(.*).$/)[1]); // "ẞ\ud83e"
const utf16Chars = string.split("");
utf16Chars.pop();
console.log(utf16Chars.join("")); // "ẞ\ud83e"
In addition, RegExp methods, as suggested in older answers, don’t match line breaks at the end:
const string = "Hello, world!\n";
console.log(string.replace(/.$/, "").endsWith("\n")); // true
console.log(string.match(/(.*).$/) === null); // true
Use the string iterator to iterate characters
Unicode-aware code utilizes the string’s iterator; see Array.from and ... spread.
string[Symbol.iterator] can be used (e.g. instead of string) as well.
Also see How to split Unicode string to characters in JavaScript.
Examples:
const string = "ẞ🦊";
console.log(Array.from(string).slice(0, -1).join("")); // "ẞ"
console.log([
...string
].slice(0, -1).join("")); // "ẞ"
Use the s and u flags on a RegExp
The dotAll or s flag makes . match line break characters, the unicode or u flag enables certain Unicode-related features.
Note that, when using the u flag, you eliminate unnecessary identity escapes, as these are invalid in a u regex, e.g. \[ is fine, as it would start a character class without the backslash, but \: isn’t, as it’s a : with or without the backslash, so you need to remove the backslash.
Examples:
const unicodeString = "ẞ🦊",
lineBreakString = "Hello, world!\n";
console.log(lineBreakString.replace(/.$/s, "").endsWith("\n")); // false
console.log(lineBreakString.match(/(.*).$/s) === null); // false
console.log(unicodeString.replace(/.$/su, "")); // ẞ
console.log(unicodeString.match(/(.*).$/su)[1]); // ẞ
// Now `split` can be made Unicode-aware:
const unicodeCharacterArray = unicodeString.split(/(?:)/su),
lineBreakCharacterArray = lineBreakString.split(/(?:)/su);
unicodeCharacterArray.pop();
lineBreakCharacterArray.pop();
console.log(unicodeCharacterArray.join("")); // "ẞ"
console.log(lineBreakCharacterArray.join("").endsWith("\n")); // false
Note that some graphemes consist of more than one code point, e.g. 🏳️‍🌈 which consists of the sequence 🏳 (U+1F3F3), VS16 (U+FE0F), ZWJ (U+200D), 🌈 (U+1F308).
Here, even Array.from will split this into four “characters”.
Matching those is made easier with the RegExp set notation and properties of strings proposal.

Using JavaScript's slice function:
let string = 'foo_bar';
string = string.slice(0, -4); // Slice off last four characters here
console.log(string);
This could be used to remove '_bar' at end of a string, of any length.

A regular expression is what you are looking for:
let str = "foo_bar";
console.log(str.replace(/_bar$/, ""));

Try this:
const myString = "Hello World!";
console.log(myString.slice(0, -1));

Performance
Today 2020.05.13 I perform tests of chosen solutions on Chrome v81.0, Safari v13.1 and Firefox v76.0 on MacOs High Sierra v10.13.6.
Conclusions
the slice(0,-1)(D) is fast or fastest solution for short and long strings and it is recommended as fast cross-browser solution
solutions based on substring (C) and substr(E) are fast
solutions based on regular expressions (A,B) are slow/medium fast
solutions B, F and G are slow for long strings
solution F is slowest for short strings, G is slowest for long strings
Details
I perform two tests for solutions A, B, C, D, E(ext), F, G(my)
for 8-char short string (from OP question) - you can run it HERE
for 1M long string - you can run it HERE
Solutions are presented in below snippet
function A(str) {
return str.replace(/.$/, '');
}
function B(str) {
return str.match(/(.*).$/)[1];
}
function C(str) {
return str.substring(0, str.length - 1);
}
function D(str) {
return str.slice(0, -1);
}
function E(str) {
return str.substr(0, str.length - 1);
}
function F(str) {
let s= str.split("");
s.pop();
return s.join("");
}
function G(str) {
let s='';
for(let i=0; i<str.length-1; i++) s+=str[i];
return s;
}
// ---------
// TEST
// ---------
let log = (f)=>console.log(`${f.name}: ${f("12345.00")}`);
[A,B,C,D,E,F,G].map(f=>log(f));
This snippet only presents soutions
Here are example results for Chrome for short string

Use regex:
let aStr = "12345.00";
aStr = aStr.replace(/.$/, '');
console.log(aStr);

How about:
let myString = "12345.00";
console.log(myString.substring(0, myString.length - 1));

1. (.*), captures any character multiple times:
console.log("a string".match(/(.*).$/)[1]);
2. ., matches last character, in this case:
console.log("a string".match(/(.*).$/));
3. $, matches the end of the string:
console.log("a string".match(/(.*).{2}$/)[1]);

https://stackoverflow.com/questions/34817546/javascript-how-to-delete-last-two-characters-in-a-string
Just use trim if you don't want spaces
"11.01 °C".slice(0,-2).trim()

Here is an alternative that i don't think i've seen in the other answers, just for fun.
var strArr = "hello i'm a string".split("");
strArr.pop();
document.write(strArr.join(""));
Not as legible or simple as slice or substring but does allow you to play with the string using some nice array methods, so worth knowing.

debris = string.split("_") //explode string into array of strings indexed by "_"
debris.pop(); //pop last element off the array (which you didn't want)
result = debris.join("_"); //fuse the remainng items together like the sun

If you want to do generic rounding of floats, instead of just trimming the last character:
var float1 = 12345.00,
float2 = 12345.4567,
float3 = 12345.982;
var MoreMath = {
/**
* Rounds a value to the specified number of decimals
* #param float value The value to be rounded
* #param int nrDecimals The number of decimals to round value to
* #return float value rounded to nrDecimals decimals
*/
round: function (value, nrDecimals) {
var x = nrDecimals > 0 ? 10 * parseInt(nrDecimals, 10) : 1;
return Math.round(value * x) / x;
}
}
MoreMath.round(float1, 1) => 12345.0
MoreMath.round(float2, 1) => 12345.5
MoreMath.round(float3, 1) => 12346.0
EDIT: Seems like there exists a built in function for this, as Paolo points out. That solution is obviously much cleaner than mine. Use parseFloat followed by toFixed

if(str.substring(str.length - 4) == "_bar")
{
str = str.substring(0, str.length - 4);
}

Via slice(indexStart, indexEnd) method - note, this does NOT CHANGE the existing string, it creates a copy and changes the copy.
console.clear();
let str = "12345.00";
let a = str.slice(0, str.length -1)
console.log(a, "<= a");
console.log(str, "<= str is NOT changed");
Via Regular Expression method - note, this does NOT CHANGE the existing string, it creates a copy and changes the copy.
console.clear();
let regExp = /.$/g
let b = str.replace(regExp,"")
console.log(b, "<= b");
console.log(str, "<= str is NOT changed");
Via array.splice() method -> this only works on arrays, and it CHANGES, the existing array (so careful with this one), you'll need to convert a string to an array first, then back.
console.clear();
let str = "12345.00";
let strToArray = str.split("")
console.log(strToArray, "<= strToArray");
let spliceMethod = strToArray.splice(str.length-1, 1)
str = strToArray.join("")
console.log(str, "<= str is changed now");

In cases where you want to remove something that is close to the end of a string (in case of variable sized strings) you can combine slice() and substr().
I had a string with markup, dynamically built, with a list of anchor tags separated by comma. The string was something like:
var str = "<a>text 1,</a><a>text 2,</a><a>text 2.3,</a><a>text abc,</a>";
To remove the last comma I did the following:
str = str.slice(0, -5) + str.substr(-4);

You can, in fact, remove the last arr.length - 2 items of an array using arr.length = 2, which if the array length was 5, would remove the last 3 items.
Sadly, this does not work for strings, but we can use split() to split the string, and then join() to join the string after we've made any modifications.
var str = 'string'
String.prototype.removeLast = function(n) {
var string = this.split('')
string.length = string.length - n
return string.join('')
}
console.log(str.removeLast(3))

Try to use toFixed
const str = "12345.00";
return (+str).toFixed(1);

Try this:
<script>
var x="foo_foo_foo_bar";
for (var i=0; i<=x.length; i++) {
if (x[i]=="_" && x[i+1]=="b") {
break;
}
else {
document.write(x[i]);
}
}
</script>
You can also try the live working example on http://jsfiddle.net/informativejavascript/F7WTn/87/.

#Jason S:
You can use slice! You just have to
make sure you know how to use it.
Positive #s are relative to the
beginning, negative numbers are
relative to the end.
js>"12345.00".slice(0,-1)
12345.0
Sorry for my graphomany but post was tagged 'jquery' earlier. So, you can't use slice() inside jQuery because slice() is jQuery method for operations with DOM elements, not substrings ...
In other words answer #Jon Erickson suggest really perfect solution.
However, your method will works out of jQuery function, inside simple Javascript.
Need to say due to last discussion in comments, that jQuery is very much more often renewable extension of JS than his own parent most known ECMAScript.
Here also exist two methods:
as our:
string.substring(from,to) as plus if 'to' index nulled returns the rest of string. so:
string.substring(from) positive or negative ...
and some other - substr() - which provide range of substring and 'length' can be positive only:
string.substr(start,length)
Also some maintainers suggest that last method string.substr(start,length) do not works or work with error for MSIE.

Use substring to get everything to the left of _bar. But first you have to get the instr of _bar in the string:
str.substring(3, 7);
3 is that start and 7 is the length.

Javascript split function not correct worked with specific regex

I have a problem. I have a string - "\,str\,i,ing" and i need to split by comma before which not have slash. For my string - ["\,str\,i", "ing"]. I'm use next regex
myString.split("[^\],", 2)
but it's doesn't worked.

Well, this is ridiculous to avoid the lack of lookbehind but seems to get the correct result.
"\\,str\\,i,ing".split('').reverse().join('').split(/,(?=[^\\])/).map(function(a){
return a.split('').reverse().join('');
}).reverse();
//=> ["\,str\,i", "ing"]

Not sure about your expected output but you are specifying string not a regex, use:
var arr = "\,str\,i,ing".split(/[^\\],/, 2);
console.log(arr);
To split using regex, wrap your regex in /..../

This is not easily possible with js, because it does not support lookbehind. Even if you'd use a real regex, it would eat the last character:
> "xyz\\,xyz,xyz".split(/[^\\],/, 2)
["xyz\\,xy", "xyz"]
If you don't want the z to be eaten, I'd suggest:
var str = "....";
return str.split(",").reduce(function(res, part) {
var l = res.length;
if (l && res[l-1].substr(-1) == "\\" || l<2)
// ^ ^^ ^
// not the first was escaped limit
res[l-1] += ","+part;
else
res.push(part);
return;
}, []);

Reading between the lines, it looks like you want to split a string by , characters that are not preceded by \ characters.
It would be really great if JavaScript had a regular expression lookbehind (and negative lookbehind) pattern, but unfortunately it does not. What it does have is a lookahead ((?=) )and negative lookahead ((?!)) pattern. Make sure to review the documentation.
You can use these as a lookbehind if you reverse the string:
var str,
reverseStr,
arr,
reverseArr;
//don't forget to escape your backslashes
str = '\\,str\\,i,ing';
//reverse your string
reverseStr = str.split('').reverse().join('');
//split the array on `,`s that aren't followed by `\`
reverseArr = reverseStr.split(/,(?!\\)/);
//reverse the reversed array, and reverse each string in the array
arr = reverseArr.reverse().map(function (val) {
return val.split('').reverse().join('');
});

You picked a tough character to match- a forward slash preceding a comma is apt to disappear while you pass it around in a string, since '\,'==','...
var s= 'My dog, the one with two \\, blue \\,eyes, is asleep.';
var a= [], M, rx=/(\\?),/g;
while((M= rx.exec(s))!= null){
if(M[1]) continue;
a.push(s.substring(0, rx.lastIndex-1));
s= s.substring(rx.lastIndex);
rx.lastIndex= 0;
};
a.push(s);
/* returned value: (Array)
My dog
the one with two \, blue \,eyes
is asleep.
*/

Find something which will not be present in your original string, say "###". Replace "\\," with it. Split the resulting string by ",". Replace "###" back with "\\,".
Something like this:
<script type="text/javascript">
var s1 = "\\,str\\,i,ing";
var s2 = s1.replace(/\\,/g,"###");
console.log(s2);
var s3 = s2.split(",");
for (var i=0;i<s3.length;i++)
{
s3[i] = s3[i].replace(/###/g,"\\,");
}
console.log(s3);
</script>
See JSFiddle

Regular Expression for formatting numbers in JavaScript

I need to display a formatted number on a web page using JavaScript. I want to format it so that there are commas in the right places. How would I do this with a regular expression? I've gotten as far as something like this:
myString = myString.replace(/^(\d{3})*$/g, "${1},");
...and then realized this would be more complex than I think (and the regex above is not even close to what I need). I've done some searching and I'm having a hard time finding something that works for this.
Basically, I want these results:
45 becomes 45
3856 becomes 3,856
398868483992 becomes 398,868,483,992
...you get the idea.

This can be done in a single regex, no iteration required. If your browser supports ECMAScript 2018, you could simply use lookaround and just insert commas at the right places:
Search for (?<=\d)(?=(\d\d\d)+(?!\d)) and replace all with ,
In older versions, JavaScript doesn't support lookbehind, so that doesn't work. Fortunately, we only need to change a little bit:
Search for (\d)(?=(\d\d\d)+(?!\d)) and replace all with \1,
So, in JavaScript, that would look like:
result = subject.replace(/(\d)(?=(\d\d\d)+(?!\d))/g, "$1,");
Explanation: Assert that from the current position in the string onwards, it is possible to match digits in multiples of three, and that there is a digit left of the current position.
This will also work with decimals (123456.78) as long as there aren't too many digits "to the right of the dot" (otherwise you get 123,456.789,012).
You can also define it in a Number prototype, as follows:
Number.prototype.format = function(){
return this.toString().replace(/(\d)(?=(\d{3})+(?!\d))/g, "$1,");
};
And then using it like this:
var num = 1234;
alert(num.format());
Credit: Jeffrey Friedl, Mastering Regular Expressions, 3rd. edition, p. 66-67

Formatting a number can be handled elegantly with one line of code.
This code extends the Number object; usage examples are included below.
Code:
Number.prototype.format = function () {
return this.toString().split( /(?=(?:\d{3})+(?:\.|$))/g ).join( "," );
};
How it works
The regular expression uses a look-ahead to find positions within the string where the only thing to the right of it is one or more groupings of three numbers, until either a decimal or the end of string is encountered. The .split() is used to break the string at those points into array elements, and then the .join() merges those elements back into a string, separated by commas.
The concept of finding positions within the string, rather than matching actual characters, is important in order to split the string without removing any characters.
Usage examples:
var n = 9817236578964235;
alert( n.format() ); // Displays "9,817,236,578,964,235"
n = 87345.87;
alert( n.format() ); // Displays "87,345.87"
Of course, the code can easily be extended or changed to handle locale considerations. For example, here is a new version of the code that automatically detects the locale settings and swaps the use of commas and periods.
Locale-aware version:
Number.prototype.format = function () {
if ((1.1).toLocaleString().indexOf(".") >= 0) {
return this.toString().split( /(?=(?:\d{3})+(?:\.|$))/g ).join( "," );
}
else {
return this.toString().split( /(?=(?:\d{3})+(?:,|$))/g ).join( "." );
}
};
Unless it's really necessary, I prefer the simplicity of the first version though.

With the caveat that Intl.NumberFormat and Number.toLocaleString() are now there for this purpose in JavaScript:
The other answers using regular expressions all break down for decimal numbers (although the authors seem to not know this because they have only tested with 1 or 2 decimal places). This is because without lookbehind, JS regular expressions have no way to know whether you are working with the block of digits before or after the decimal point. That leaves two ways to address this with JS regular expressions:
Know whether there is a decimal point in the number, and use different regular expressions depending on that:
/(\d)(?=(\d{3})+$)/g for integers
/(\d)(?=(\d{3})+\.)/g for decimals
Use two regular expressions, one to match the decimal portion, and a second to do a replace on it.
function format(num) {
return num.toString().replace(/^[+-]?\d+/, function(int) {
return int.replace(/(\d)(?=(\d{3})+$)/g, '$1,');
});
}
console.log(format(332432432))
console.log(format(332432432.3432432))
console.log(format(-332432432))
console.log(format(1E6))
console.log(format(1E-6))

function numberWithCommas(x) {
return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}
var num=numberWithCommas(2000000); //any number
console.log(num);
enter code here
Try this

// You might want to take decimals into account
Number.prototype.commas= function(){
var s= '', temp,
num= this.toString().split('.'), n=num[0];
while(n.length> 3){
temp= n.substring(n.length-3);
s= ','+temp+s;
n= n.slice(0, -3);
}
if(n) s= n+s;
if(num[1]) s+='.'+num[1];
return s;
}
var n= 10000000000.34;
n.commas() = returned value: (String) 10,000,000,000.34

underscore.string has a nice implementation.
I've amended it slightly to accept numeric strings.
function numberFormat(number, dec, dsep, tsep) {
if (isNaN(number) || number == null) return '';
number = parseFloat(number).toFixed(~~dec);
tsep = typeof tsep == 'string' ? tsep : ',';
var parts = number.split('.'),
fnums = parts[0],
decimals = parts[1] ? (dsep || '.') + parts[1] : '';
return fnums.replace(/(\d)(?=(?:\d{3})+$)/g, '$1' + tsep) + decimals;
}
console.log(numberFormat(123456789))
console.log(numberFormat(123456789.123456789))
console.log(numberFormat(-123456789))
console.log(numberFormat(1E6))
console.log(numberFormat(1E-6))
console.log('---')
console.log(numberFormat(123456789, 6, ',', '_'))
console.log(numberFormat(123456789.123456789, 6, ',', '_'))
console.log(numberFormat(-123456789, 6, ',', '_'))
console.log(numberFormat(1E6, 6, ',', '_'))
console.log(numberFormat(1E-6, 6, ',', '_'))

One RegExp for integers and decimals:
// Formats number 1234.5678 into string "1 234.5678".
function formatNumber(number: number): string {
return number.toString().replace(/(?<!(\.\d*|^.{0}))(?=(\d{3})+(?!\d))/g, ' ');
}
console.log(formatNumber(1234.5678)); // "1 234.5678"
console.log(formatNumber(123)); // "123"
console.log(formatNumber(123.45678)); // "123.45678"
console.log(formatNumber(123456789.11111111)); // "123 456 789.1111111"

Try something like this:
function add_commas(numStr)
{
numStr += '';
var x = numStr.split('.');
var x1 = x[0];
var x2 = x.length > 1 ? '.' + x[1] : '';
var rgx = /(\d+)(\d{3})/;
while (rgx.test(x1)) {
x1 = x1.replace(rgx, '$1' + ',' + '$2');
}
return x1 + x2;
}

If you really want a regex, you can use two in a while loop:
while(num.match(/\d{4}/)) {
num = num.replace(/(\d{3})(,\d|$)/, ',$1$2');
}
And if you want to be fancy, you can format numbers with decimal points too:
while(num.match(/\d{4}(\,|\.)/)) {
num = num.replace(/(\d{3})(,\d|$|\.)/, ',$1$2');
}
Edit:
You can also do this with 2 regular expressions and no loop, splits, joins, etc:
num = num.replace(/(\d{1,2}?)((\d{3})+)$/, "$1,$2");
num = num.replace(/(\d{3})(?=\d)/g, "$1,");
The first regex puts a comma after the first 1 or 2 digits if the remaining number of digits is divisible by three. The second regex places a comma after every remaining group of 3 digits.
These won't work with decimals, but they work great for positive and negative integers.
Test output:
45
3,856
398,868,483,992
635
12,358,717,859,918,856
-1,388,488,184

Someone mentioned that lookbehind isn't possible in Javascript RegExp. Here is a great page that explains how to use lookaround (lookahead and lookbehind).
http://www.regular-expressions.info/lookaround.html

I think you would necessarily have to do multiple passes to achieve this with regular expressions. Try the following:
Run a regex for one digit followed by 3 digits.
If that regex matches, replace it with the first digit, then a comma, then the next 3 digits.
Repeat until (1) finds no matches.

Iteration isn't necessary
function formatNumber(n, separator) {
separator = separator || ",";
n = n.toString()
.split("").reverse().join("")
.replace(/(\d{3})/g, "$1" + separator)
.split("").reverse().join("");
// Strings that have a length that is a multiple of 3 will have a leading separator
return n[0] == separator ? n.substr(1) : n;
}
var testCases = [1, 45, 2856, 398868483992];
for ( var i in testCases ) {
if ( !ns.hasOwnProperty(i) ) { continue; }
console.info(testCases[i]);
console.log(formatNumber(testCases[i]));
}
Results
1
1
45
45
2856
2,856
398868483992
398,868,483,992

First reverse a character array, then add commas after every third number unless it's just before the end of the string or before a - sign. Then reverse the character array again and make it a string again.
function add_commas(numStr){
return numStr.split('').reverse().join('').replace(/(\d{3})(?=[^$|^-])/g, "$1,").split('').reverse().join('');
}

Brandon,
I didn't see too many answers working the regex from the decimal point back, so I thought I might chime in.
I wondered if there is any elegant benefit to re-writing the regexp to scan from the back forward...
function addCommas(inputText) {
// pattern works from right to left
var commaPattern = /(\d+)(\d{3})(\.\d*)*$/;
var callback = function (match, p1, p2, p3) {
return p1.replace(commaPattern, callback) + ',' + p2 + (p3 || '');
};
return inputText.replace(commaPattern, callback);
}
>> Fiddle Demo <<
This accounts for any decimal place.

After so much searching, I generate a regex which accepts all formats
(\d+[-, ,(]{0,3}\d+[-, ,(,)]{0,3}\d+[-, ,(,)]{0,3}\d+[)]{0,2})