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JavaScript: Take first three characters of each word in string and put "_" after each word

What I would like to achieve is take a string:
var string = "Hello there my friend";
And return a formatted string as follows:
"HEL_THE_MY_FRI"
So I am trying to take the first three characters of each word in a string and add an underscore after each. The capitalize is easy :) .toUpperCase()

You could use replace for that:
var string = "Hello there my friend";
var result = string.toUpperCase().replace(/\b(\S{1,3})\S*/g, '$1').replace(/ /g, '_');
console.log(result);

Since you didn't provide any code for what you've tried so far, the steps you'd take are:
split the string on spaces
loop over your array of words
get a substring from each word 3 characters long
uppercase the substring
append it to your new string
add an underscore if it isn't the last word in your array
var phrase = 'this is my string';
var words = phrase.split(' ');
var result = '';
for (var i = 0; i < words.length; i++) {
var word = words[i];
result += word.substring(0, 3).toUpperCase();
if (i < words.length - 1) {
result += '_';
}
}
console.log(result);

"One-line" solution using String.replace(), String.toUpperCase() and String.slice() functions:
var string = "Hello there my friend",
replaced = string.replace(/\b(\w{1,3})(\w+\s?|\s)/g, '$1_').toUpperCase().slice(0,-1);
console.log(replaced);

console.log("Hello there my friend".split(" ").map((a)=>a.substring(0, 3)).join("_").toUpperCase());

How can I replace single digit numbers within a string without affecting 2 digit numbers in that string

I'm working to update this function which currently takes the content and replaces any instance of the target with the substitute.
var content = textArea.value; //should be in string form
var target = targetTextArea.value;
var substitute = substituteTextArea.value;
var expression = new RegExp(target, "g"); //In order to do a global replace(replace more than once) we have to use a regex
content = content.replace(expression, substitute);
textArea.value = content.split(",");
This code somewhat works... given the input "12,34,23,13,22,1,17" and told to replace "1" with "99" the output would be "992,34,23,993,22,99,997" when it should be "12,34,23,13,22,99,17". The replace should only be performed when the substitute is equal to the number, not a substring of the number.
I dont understand the comment about the regex needed to do a global replace, I'm not sure if that's a clue?
It's also worth mentioning that I'm dealing with a string separated by either commas or spaces.
Thanks!

You could do this if regex is not a requirement
var str = "12,34,23,13,22,1,17";
var strArray = str.split(",");
for(var item in strArray)
{
if(strArray[item] === "1")
{
strArray[item] = "99"
}
}
var finalStr = strArray.join()
finalStr will be "12,34,23,13,22,99,17"

Try with this
var string1 = "12,34,23,13,22,1,17";
var pattern = /1[^\d]/g;
// or pattern = new RegExp(target+'[^\\d]', 'g');
var value = substitute+",";//Replace comma with space if u uses space in between
string1 = string1.replace(pattern, value);
console.log(string1);

Try this
target = target.replace(/,1,/g, ',99,');
Documentation

EDIT: When you say: "a string separated by either commas or spaces"
Do you mean either a string with all commas, or a string with all spaces?
Or do you have 1 string with both commas and spaces?
My answer has no regex, nothing fancy ...
But it looks like you haven't got an answer that works yet
<div id="log"></div>
<script>
var myString = "12,34,23,13,22,1,17";
var myString2 = "12 34 23 13 22 1 17";
document.getElementById('log').innerHTML += '<br/>with commas: ' + replaceItem(myString, 1, 99);
document.getElementById('log').innerHTML += '<br/>with spaces: ' + replaceItem(myString2, 1, 99);
function replaceItem(string, needle, replace_by) {
var deliminator = ',';
// split the string into an array of items
var items = string.split(',');
// >> I'm dealing with a string separated by either commas or spaces
// so if split had no effect (no commas found), we try again with spaces
if(! (items.length > 1)) {
deliminator = ' ';
items = string.split(' ');
}
for(var i=0; i<items.length; i++) {
if(items[i] == needle) {
items[i] = replace_by;
}
}
return items.join(deliminator);
}
</script>

Regex to remove all characters that are repeated

I'm looking for a regex that will remove all characters that have been repeated in a string. I already solved this using a loop. Just wondering if there is a regex that can do the same.
this is what i have so far:
function onlyUnique(str) {
var re = /(.)(?=.*\1)/g
return str.replace(re, '');
}
This string:
"rc iauauc!gcusa_usdiscgaesracg"
should end up as this:
" !_de"

You can use Array#filter with Array#indexOf and Array#lastIndexOf to check if the element is repeated.
var str = "rc iauauc!gcusa_usdiscgaesracg";
// Split to get array
var arr = str.split('');
// Filter splitted array
str = arr.filter(function (e) {
// If index and lastIndex are equal, the element is not repeated
return arr.indexOf(e) === arr.lastIndexOf(e);
}).join(''); // Join to get string from array
console.log(str);
document.write(str);

well, no idea if regex can do that, but you could work it out using for loop, like:
function unikChars(str) {
store = [];
for (var a = 0, len = str.length; a < len; a++) {
var ch = str.charAt(a);
if (str.indexOf(ch) == a && str.indexOf(ch, a + 1) == -1) {
store.push(ch);
}
}
return store.join("");
}
var str = 'rc iauauc!gcusa_usdiscgaesracg';
console.log(unikChars(str)); //gives !_de
Demo:: jsFiddle

Your regex searches pairs of duplicated characters and only removes the first one. Therefore, the latest duplicate won't be removed.
To address this problem, you should remove all duplicates simultaneously, but I don't think you can do this with a single replace.
Instead, I would build a map which counts the occurrences of each character, and then iterate the string again, pushing the characters that appeared only once to a new string:
function onlyUnique(str) {
var map = Object.create(null);
for(var i=0; i<str.length; ++i)
map[str[i]] = (map[str[i]] || 0) + 1;
var chars = [];
for(var i=0; i<str.length; ++i)
if(map[str[i]] === 1)
chars.push(str[i]);
return chars.join('');
}
Unlike indexOf, searches in the hash map are constant on average. So the cost of a call with a string of n characters will be n.

If you want to do it with a regex, you can use your own regex with a callback function inside a replace.
var re = /(.)(?=.*\1)/g;
var str = 'rc iauauc!gcusa_usdiscgaesracg';
var result = str;
str.replace(re, function(m, g1) {
result = result.replace(RegExp(g1.replace(/[.*+?^${}()|[\]\\]/g, "\\$&"), "g"), '');
});
document.getElementById("r").innerHTML = "'" + result + "'";
<div id="r"/>
The idea is: get the duplicated character, and remove it from the input string. Note that escaping is necessary if the character might be a special regex metacharacter (thus, g1.replace(/[.*+?^${}()|[\]\\]/g, "\\$&") is used).
Another idea belongs to Washington Guedes in his deleted answer, I just add my own implementation here (with removing duplicate symbols from the character class and escaping special regex chars):
var s = "rc iauauc!gcusa_u]sdiscgaesracg]";
var delimiters= '[' + s.match(/(.)(?=.*\1)/g).filter(function(value, index, self) { // find all repeating chars
return self.indexOf(value) === index; // get unique values only
}).join('').replace(/[.*+?^${}()|[\]\\]/g, "\\$&") + ']'; // escape special chars
var regex = new RegExp(delimiters, 'g'); // build the global regex from the delimiters
var result = s.replace(regex, ''); // obtain the result
document.getElementById("r2").innerHTML = "'" + result + "'";
<div id="r2"/>
NOTE: if you want to support newline symbols as well, replace . with [^] or [\s\S] inside the regex pattern.

function onlyUnique(str) {
// match the characters you want to remove
var match = str.match(/(.)(?=.*\1)/g);
if (match) {
// build your regex pattern
match = '[' + match.join('') + ']';
}
// if string is already unique return the string
else {
return str
}
// create a regex with the characters you want to remove
var re = new RegExp(match, 'g');
return str.replace(re, '');
}

Replacing multiple characters in a string with a string rewrites characters

I have a variable (in this example var str = "I!%1$s-I!%2$s TTL!%3$s";), in which I want to replace the % with elements from an array (var regex = ['aaa', 'bbb', 'ccc'];).
I google around a bit and found this solution, but I'm having trouble implementing it. My problem is that I want to replace a single character with multiple characters, and then continue the string, but this just overwrites the characters. I actually have no idea why.
Any help is appreciated, my code below
String.prototype.replaceAt = function(index, character) {
return this.substr(0, index) + character + this.substr(index + character.length);
}
var str = "I!%1$s-I!%2$s TTL!%3$s";
var regex = ['replace', 'replace', 'replace'];
//find position of %
var find = /%/gi,
result, pos = [];
while ((result = find.exec(str))) {
pos.push(result.index);
}
//replace % with regex elements
for (x = 0; x < pos.length; x++) {
str = str.replaceAt(pos[x], regex[x]);
}
document.write(str);

Use replacement function, like this
var str = "I!%1$s-I!%2$s TTL!%3$s";
var regex = ['[123]', '[456]', '[789]'];
console.log(str.replace(/%(\d+)/g, function(match, group1) {
return regex[parseInt(group1) - 1] + group1;
}));
// I![123]1$s-I![456]2$s TTL![789]3$s
The RegEx /%(\d+)/g matches anything of the pattern % followed by one or more digits. And it captures the digits as a group. Then the exact match and the group is passed to the function to get the actual replacement. In the function, you convert the group to a number with parseInt and return the respective value from the regex array.

How to count the number of characters without spaces?

I'm new to this, so please understand me;/
I'm creating an app in appery.io and it has to count the number of letters of text inserted by the app user(without spaces).
I have an input field created(input), a button to press and show the result in a label(result)
the code for the button:
var myString = getElementById("input");
var length = myString.length;
Apperyio('result').text(length);
Can you please tell me what is wrong?

To ignore a literal space, you can use regex with a space:
// get the string
let myString = getElementById("input").value;
// use / /g to remove all spaces from the string
let remText = myString.replace(/ /g, "");
// get the length of the string after removal
let length = remText.length;
To ignore all white space(new lines, spaces, tabs) use the \s quantifier:
// get the string
let myString = getElementById("input").value;
// use the \s quantifier to remove all white space
let remText = myString.replace(/\s/g, "")
// get the length of the string after removal
let length = remText.length;

Use this:
var myString = getElementById("input").value;
var withoutSpace = myString.replace(/ /g,"");
var length = withoutSpace.length;

count = 0;
const textLenght = 'ABC ABC';
for (var i = 0, len = textLenght.length; i < len; i++) {
if (textLenght[i] !== ' ')
count++;
}

You can count white spaces and subtract it from lenght of string for example
var my_string = "John Doe's iPhone6";
var spaceCount = (my_string.split(" ").length - 1);
console.log(spaceCount);
console.log('total count:- ', my_string.length - spaceCount)