extracting a string out of another url or string - javascript

I want to extract the store/brand names out of the url or some title string.
so the url could be something like
"http://www.store1.com/brand1-Transform-Ultra-Prepaid-/"
and title could be " brand1 Transform Ultra Prepaid Phone "
I will keep the possible store names in an array like
var store_array = ['store1', 'brand1', 'brand2']
lets say if i search the above url or title, i should get the store1 and brand1 as a result.
how to do this in jquery, am beginner, please explain me in detail.
my initial idea is that i should below, but not sure. please help.
$.each( store_array, function(index, value) {
//what to do here
});

You can do:
var url = 'http://www.store1.com/brand1-Transform-Ultra-Prepaid-/',
path = url.split('/');
var store_array = path[path.length-2].split('-');
Demo: http://jsfiddle.net/jcGsp/
This all depends on how dynamic you want it to be, another options would be a regexp:
var url = 'http://www.store1.com/brand1-Transform-Ultra-Prepaid-/';
var store_array = url.replace(/http:\/\/www.store1.com\/([^\/]+)\//,'$1').split('-');
Demo: http://jsfiddle.net/fSpr3/

you can use the split function:
let's say the url is:
url=window.location.href;
url.split('http://www.store1.com/');
title=url[1];
if the word needed from "brand1-Transform-Ultra-Prepaid-" is "brand1" then split this again with:
title.split('-');
fixed_title=title[0];

I would define a function to do the matching, and run it on the strings I am interested in
function findMatches( str ){
return store_array.filter( function( el ){
return new RegExp( "\b"+el+"\b", "i" ).test( str );
});
}
var results1 = findMatches( 'http://www.store1.com/' );
var results2 = findMatches( " brand1 Transform Ultra Prepaid Phone " );
//etc
The \b ensures 'store1' etc are complete words (so, 'store1' wouldn't match 'megastore1') and the /i makes it case insensitive.
array.filter runs a function on every member of an array and returns a copy of the array with only those members for whose the function returns true. Note that array.filter is IE9 and above (you didn't specify the platform), for other browsers there is anice polyfill here https://gist.github.com/1031656
The findMatches function goes through all the strings in the list, turns them into regular expressions, and checks whether it is found in the string. If you have a lot of test string, it may be more efficient to run indexof
function findMatches( str ){
return store_array.filter( function( el ){
return ( "-1" !== str.indexOf( el ) );
});
}
Either will work. Note that this is not using jQuery, just plain JS (albeit ECMA5)

Related

Remove item from array containing text [duplicate]

I need to search an array in JavaScript. The search would be for only part of the string to match as the string would have additional components. I would then need to return the successfully matched array element with the full string.
Example:
const windowArray = [ "item", "thing", "id-3-text", "class" ];
I need to search for the array element with "id-" in it and I need to pull the rest of the text in the element as well (i.e. "id-3-text").
How do I do that?
If you're able to use Underscore.js in your project, the _.filter() array function makes this a snap:
// find all strings in array containing 'thi'
var matches = _.filter(
[ 'item 1', 'thing', 'id-3-text', 'class' ],
function( s ) { return s.indexOf( 'thi' ) !== -1; }
);
The iterator function can do whatever you want as long as it returns true for matches. Works great.
Update 2017-12-03:
This is a pretty outdated answer now. Maybe not the most performant option in a large batch, but it can be written a lot more tersely and use native ES6 Array/String methods like .filter() and .includes() now:
// find all strings in array containing 'thi'
const items = ['item 1', 'thing', 'id-3-text', 'class'];
const matches = items.filter(s => s.includes('thi'));
Note: There's no <= IE11 support for String.prototype.includes() (Edge works, mind you), but you're fine with a polyfill, or just fall back to indexOf().
People here are making this waaay too difficult. Just do the following...
myArray.findIndex(element => element.includes("substring"))
findIndex() is an ES6 higher order method that iterates through the elements of an array and returns the index of the first element that matches some criteria (provided as a function). In this case I used ES6 syntax to declare the higher order function. element is the parameter of the function (which could be any name) and the fat arrow declares what follows as an anonymous function (which does not need to be wrapped in curly braces unless it takes up more than one line).
Within findIndex() I used the very simple includes() method to check if the current element includes the substring that you want.
The simplest way to get the substrings array from the given array is to use filter and includes:
myArray.filter(element => element.includes("substring"));
The above one will return an array of substrings.
myArray.find(element => element.includes("substring"));
The above one will return the first result element from the array.
myArray.findIndex(element => element.includes("substring"));
The above one will return the index of the first result element from the array.
In your specific case, you can do it just with a boring old counter:
var index, value, result;
for (index = 0; index < windowArray.length; ++index) {
value = windowArray[index];
if (value.substring(0, 3) === "id-") {
// You've found it, the full text is in `value`.
// So you might grab it and break the loop, although
// really what you do having found it depends on
// what you need.
result = value;
break;
}
}
// Use `result` here, it will be `undefined` if not found
But if your array is sparse, you can do it more efficiently with a properly-designed for..in loop:
var key, value, result;
for (key in windowArray) {
if (windowArray.hasOwnProperty(key) && !isNaN(parseInt(key, 10))) {
value = windowArray[key];
if (value.substring(0, 3) === "id-") {
// You've found it, the full text is in `value`.
// So you might grab it and break the loop, although
// really what you do having found it depends on
// what you need.
result = value;
break;
}
}
}
// Use `result` here, it will be `undefined` if not found
Beware naive for..in loops that don't have the hasOwnProperty and !isNaN(parseInt(key, 10)) checks; here's why.
Off-topic:
Another way to write
var windowArray = new Array ("item","thing","id-3-text","class");
is
var windowArray = ["item","thing","id-3-text","class"];
...which is less typing for you, and perhaps (this bit is subjective) a bit more easily read. The two statements have exactly the same result: A new array with those contents.
Just search for the string in plain old indexOf
arr.forEach(function(a){
if (typeof(a) == 'string' && a.indexOf('curl')>-1) {
console.log(a);
}
});
The simplest vanilla javascript code to achieve this is
var windowArray = ["item", "thing", "id-3-text", "class", "3-id-text"];
var textToFind = "id-";
//if you only want to match id- as prefix
var matches = windowArray.filter(function(windowValue){
if(windowValue) {
return (windowValue.substring(0, textToFind.length) === textToFind);
}
}); //["id-3-text"]
//if you want to match id- string exists at any position
var matches = windowArray.filter(function(windowValue){
if(windowValue) {
return windowValue.indexOf(textToFind) >= 0;
}
}); //["id-3-text", "3-id-text"]
For a fascinating examination of some of the alternatives and their efficiency, see John Resig's recent posts:
JavaScript Trie Performance Analysis
Revised JavaScript Dictionary Search
(The problem discussed there is slightly different, with the haystack elements being prefixes of the needle and not the other way around, but most solutions are easy to adapt.)
let url = item.product_image_urls.filter(arr=>arr.match("homepage")!==null)
Filter array with string match. It is easy and one line code.
ref:
In javascript, how do you search an array for a substring match
The solution given here is generic unlike the solution 4556343#4556343, which requires a previous parse to identify a string with which to join(), that is not a component of any of the array strings.
Also, in that code /!id-[^!]*/ is more correctly, /![^!]*id-[^!]*/ to suit the question parameters:
"search an array ..." (of strings or numbers and not functions, arrays, objects, etc.)
"for only part of the string to match " (match can be anywhere)
"return the ... matched ... element" (singular, not ALL, as in "... the ... elementS")
"with the full string" (include the quotes)
... NetScape / FireFox solutions (see below for a JSON solution):
javascript: /* "one-liner" statement solution */
alert(
["x'!x'\"id-2",'\' "id-1 "', "item","thing","id-3-text","class" ] .
toSource() . match( new RegExp(
'[^\\\\]("([^"]|\\\\")*' + 'id-' + '([^"]|\\\\")*[^\\\\]")' ) ) [1]
);
or
javascript:
ID = 'id-' ;
QS = '([^"]|\\\\")*' ; /* only strings with escaped double quotes */
RE = '[^\\\\]("' +QS+ ID +QS+ '[^\\\\]")' ;/* escaper of escaper of escaper */
RE = new RegExp( RE ) ;
RA = ["x'!x'\"id-2",'\' "id-1 "', "item","thing","id-3-text","class" ] ;
alert(RA.toSource().match(RE)[1]) ;
displays "x'!x'\"id-2".
Perhaps raiding the array to find ALL matches is 'cleaner'.
/* literally (? backslash star escape quotes it!) not true, it has this one v */
javascript: /* purely functional - it has no ... =! */
RA = ["x'!x'\"id-2",'\' "id-1 "', "item","thing","id-3-text","class" ] ;
function findInRA(ra,id){
ra.unshift(void 0) ; /* cheat the [" */
return ra . toSource() . match( new RegExp(
'[^\\\\]"' + '([^"]|\\\\")*' + id + '([^"]|\\\\")*' + '[^\\\\]"' ,
'g' ) ) ;
}
alert( findInRA( RA, 'id-' ) . join('\n\n') ) ;
displays:
"x'!x'\"id-2"
"' \"id-1 \""
"id-3-text"
Using, JSON.stringify():
javascript: /* needs prefix cleaning */
RA = ["x'!x'\"id-2",'\' "id-1 "', "item","thing","id-3-text","class" ] ;
function findInRA(ra,id){
return JSON.stringify( ra ) . match( new RegExp(
'[^\\\\]"([^"]|\\\\")*' + id + '([^"]|\\\\")*[^\\\\]"' ,
'g' ) ) ;
}
alert( findInRA( RA, 'id-' ) . join('\n\n') ) ;
displays:
["x'!x'\"id-2"
,"' \"id-1 \""
,"id-3-text"
wrinkles:
The "unescaped" global RegExp is /[^\]"([^"]|\")*id-([^"]|\")*[^\]"/g with the \ to be found literally. In order for ([^"]|\")* to match strings with all "'s escaped as \", the \ itself must be escaped as ([^"]|\\")*. When this is referenced as a string to be concatenated with id-, each \ must again be escaped, hence ([^"]|\\\\")*!
A search ID that has a \, *, ", ..., must also be escaped via .toSource() or JSON or ... .
null search results should return '' (or "" as in an EMPTY string which contains NO "!) or [] (for all search).
If the search results are to be incorporated into the program code for further processing, then eval() is necessary, like eval('['+findInRA(RA,ID).join(',')+']').
--------------------------------------------------------------------------------
Digression:
Raids and escapes? Is this code conflicted?
The semiotics, syntax and semantics of /* it has no ... =! */ emphatically elucidates the escaping of quoted literals conflict.
Does "no =" mean:
"no '=' sign" as in javascript:alert('\x3D') (Not! Run it and see that there is!),
"no javascript statement with the assignment operator",
"no equal" as in "nothing identical in any other code" (previous code solutions demonstrate there are functional equivalents),
...
Quoting on another level can also be done with the immediate mode javascript protocol URI's below. (// commentaries end on a new line (aka nl, ctrl-J, LineFeed, ASCII decimal 10, octal 12, hex A) which requires quoting since inserting a nl, by pressing the Return key, invokes the URI.)
javascript:/* a comment */ alert('visible') ;
javascript:// a comment ; alert( 'not' ) this is all comment %0A;
javascript:// a comment %0A alert('visible but %\0A is wrong ') // X %0A
javascript:// a comment %0A alert('visible but %'+'0A is a pain to type') ;
Note: Cut and paste any of the javascript: lines as an immediate mode URI (at least, at most?, in FireFox) to use first javascript: as a URI scheme or protocol and the rest as JS labels.
I've created a simple to use library (ss-search) which is designed to handle objects, but could also work in your case:
search(windowArray.map(x => ({ key: x }), ["key"], "SEARCH_TEXT").map(x => x.key)
The advantage of using this search function is that it will normalize the text before executing the search to return more accurate results.
Another possibility is
var res = /!id-[^!]*/.exec("!"+windowArray.join("!"));
return res && res[0].substr(1);
that IMO may make sense if you can have a special char delimiter (here i used "!"), the array is constant or mostly constant (so the join can be computed once or rarely) and the full string isn't much longer than the prefix searched for.
I think this may help you. I had a similar issue. If your array looks like this:
var array = ["page1","1973","Jimmy"];
You can do a simple "for" loop to return the instance in the array when you get a match.
var c;
for (i = 0; i < array.length; i++) {
if (array[i].indexOf("page") > -1){
c = i;}
}
We create an empty variable, c to host our answer.
We then loop through the array to find where the array object (e.g. "page1") matches our indexOf("page"). In this case, it's 0 (the first result)
Happy to expand if you need further support.
Use this function for search substring Item.
function checkItem(arrayItem, searchItem) {
return arrayItem.findIndex(element => element.includes(searchItem)) >= 0
}
function getItem(arrayItem, getItem) {
return arrayItem.filter(element => element.includes(getItem))
}
var arrayItem = ["item","thing","id-3-text","class"];
console.log(checkItem(arrayItem, "id-"))
console.log(checkItem(arrayItem, "vivek"))
console.log(getItem(arrayItem, "id-"))
Here's your expected snippet which gives you the array of all the matched values:
var windowArray = new Array ("item","thing","id-3-text","class");
var result = [];
windowArray.forEach(val => {
if(val && val.includes('id-')) {
result.push(val);
}
});
console.log(result);
this worked for me .
const filterData = this.state.data2.filter(item=>((item.name.includes(text)) || (item.surname.includes(text)) || (item.email.includes(text)) || (item.userId === Number(text))) ) ;

How to obtain index of subpattern in JavaScript regexp?

I wrote a regular expression in JavaScript for searching searchedUrl in a string:
var input = '1234 url( test ) 5678';
var searchedUrl = 'test';
var regexpStr = "url\\(\\s*"+searchedUrl+"\\s*\\)";
var regex = new RegExp(regexpStr , 'i');
var match = input.match(regex);
console.log(match); // return an array
Output:
["url( test )", index: 5, input: "1234 url( test ) 5678"]
Now I would like to obtain position of the searchedUrl (in the example above it is the position of test in 1234 url( test ) 5678.
How can I do that?
As far as I could tell it wasn't possible to get the offset of a sub-match automatically, you have to do the calculation yourself using either lastIndex of the RegExp, or the index property of the match object returned by exec(). Depending on which you use you'll either have to add or subtract the length of groups leading up to your sub-match. However, this does mean you have to group the first or last part of the Regular Expression, up to the pattern you wish to locate.
lastIndex only seems to come into play when using the /g/ global flag, and it will record the index after the entire match. So if you wish to use lastIndex you'll need to work backwards from the end of your pattern.
For more information on the exec() method, see here:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/exec
The following succinctly shows the solution in operation:
var str = '---hello123';
var r = /([a-z]+)([0-9]+)/;
var m = r.exec( str );
alert( m.index + m[1].length ); // will give the position of 123
update
This would apply to your issue using the following:
var input = '1234 url( test ) 5678';
var searchedUrl = 'test';
var regexpStr = "(url\\(\\s*)("+searchedUrl+")\\s*\\)";
var regex = new RegExp(regexpStr , 'i');
var match = regex.exec(input);
Then to get the submatch offset you can use:
match.index + match[1].length
match[1] now contains url( (plus two spaces) due to the bracket grouping which allows us to tell the internal offset.
update 2
Obviously things are a little more complicated if you have patterns in the RegExp, that you wish to group, before the actual pattern you want to locate. This is just a simple act of adding together each group length.
var s = '~- [This may or may not be random|it depends on your perspective] -~';
var r = /(\[)([a-z ]+)(\|)([a-z ]+)(\])/i;
var m = r.exec( s );
To get the offset position of it depends on your perspective you would use:
m.index + m[1].length + m[2].length + m[3].length;
Obviously if you know the RegExp has portions that never change length, you can replace those with hard coded numeric values. However, it's probably best to keep the above .length checks, just in case you — or someone else — ever changes what your expression matches.
JS doesn't have a direct way to get the index of a subpattern/capturing group. But you can work around that with some tricks. For example:
var reStr = "(url\\(\\s*)" + searchedUrl + "\\s*\\)";
var re = new RegExp(reStr, 'i');
var m = re.exec(input);
if(m){
var index = m.index + m[1].length;
console.log("url found at " + index);
}
You can add the 'd' flag to the regex in order to generate indices for substring matches.
const input = '1234 url( test ) 5678';
const searchedUrl = 'test';
const regexpStr = "url\\(\\s*("+searchedUrl+")\\s*\\)";
const regex = new RegExp(regexpStr , 'id');
const match = regex.exec(input).indices[1]
console.log(match); // return [11, 15]
You don't need the index.
This is a case where providing just a bit more information would have gotten a much better answer. I can't fault you for it; we're encouraged to create simple test cases and cut out irrelevant detail.
But one important item was missing: what you plan to do with that index. In the meantime, we were all chasing the wrong problem. :-)
I had a feeling something was missing; that's why I asked you about it.
As you mentioned in the comment, you want to find the URL in the input string and highlight it in some way, perhaps by wrapping it in a <b></b> tag or the like:
'1234 url( <b>test</b> ) 5678'
(Let me know if you meant something else by "highlight".)
You can use character indexes to do that, however there is a much easier way using the regular expression itself.
Getting the index
But since you asked, if you did need the index, you could get it with code like this:
var input = '1234 url( test ) 5678';
var url = 'test';
var regexpStr = "^(.*url\\(\\s*)"+ url +"\\s*\\)";
var regex = new RegExp( regexpStr , 'i' );
var match = input.match( regex );
var start = match[1].length;
This is a bit simpler than the code in the other answers, but any of them would work equally well. This approach works by anchoring the regex to the beginning of the string with ^ and putting all the characters before the URL in a group with (). The length of that group string, match[1], is your index.
Slicing and dicing
Once you know the starting index of test in your string, you could use .slice() or other string methods to cut up the string and insert the tags, perhaps with code something like this:
// Wrap url in <b></b> tag by slicing and pasting strings
var output =
input.slice( 0, start ) +
'<b>' + url + '</b>' +
input.slice( start + url.length );
console.log( output );
That will certainly work, but it is really doing things the hard way.
Also, I left out some error handling code. What if there is no matching URL? match will be undefined and the match[1] will fail. But instead of worrying about that, let's see how we can do it without any character indexing at all.
The easy way
Let the regular expression do the work for you. Here's the whole thing:
var input = '1234 url( test ) 5678';
var url = 'test';
var regexpStr = "(url\\(\\s*)(" + url + ")(\\s*\\))";
var regex = new RegExp( regexpStr , 'i' );
var output = input.replace( regex, "$1<b>$2</b>$3" );
console.log( output );
This code has three groups in the regular expression, one to capture the URL itself, with groups before and after the URL to capture the other matching text so we don't lose it. Then a simple .replace() and you're done!
You don't have to worry about any string lengths or indexes this way. And the code works cleanly if the URL isn't found: it returns the input string unchanged.

how to get the parameter value from the url in javascript? [duplicate]

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
How can I get a specific parameter from location.search?
I have a url like the following.
http://localhost/xxx.php?tPath=&pid=37
I want to get the pid=37 but by its name because on time the url is like above and then when page refreshed then the url becomes like the following.
http://localhost/xxx.php?tPath=&action=xxx&pid=37&value=13&fname=aaaa&fone=4321122
So I want to get the pid=37. It might be a function to which I pass the pid as a parameter and it returns its value.
How will I do this?
Take a look at this or follow a solution like this:
function getParam( name )
{
name = name.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");
var regexS = "[\\?&]"+name+"=([^&#]*)";
var regex = new RegExp( regexS );
var results = regex.exec( window.location.href );
if( results == null )
return "";
else
return results[1];
}
var frank_param = getParam( 'pid' );
Use the following function
function getParameterValue(name)
{
name = name.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");
var regexS = "[\\?&]"+name+"=([^&#]*)";
var regex = new RegExp( regexS );
var results = regex.exec( window.location.href );
if( results == null ) return "";
else return results[1];
}
Well, there are three answers already, which all use regex. But a regex is really the wrong tool for this job. As someone famously said, some people, when they have a problem, think, "I know, I'll use a regular expression!" Now they have two problems. Here are some of the reasons those answers are wrong:
If the "name" you're looking for has regex characters in it, you need to escape them, and all of the regexen fail if the URL uses an ampersand in the path part (not RFC-conformant, but some people might do it anyway).
They all fail if the parameter you're looking for has characters that are meaningful in a regex (for example, $).
Oh, and they all fail to account for multiple results (e.g., path?foo=bar&foo=baz), which is perfectly valid and relatively common in querystrings.
This really is a job for plain-ol' string functions, as given in this answer. I'd have written the function a little differently stylistically, but the algorithm is sound.
check this small utility http://jsfiddle.net/gwB2C/2/
usage :
var up = new URLParser();
var urlObj = up.parse('http://localhost/xxx.php?tPath=&action=xxx&pid=37&value=13&fname=aaaa&fone=4321122');
alert(urlObj.params['fname']); //alerts 'aaaa'
value of urlObj :
baseURL: "http://localhost/xxx.php"
params:{
action: "xxx"
fname: "aaaa"
fone: "4321122"
pid: "37"
tPath: ""
value: "13"
}
queryString: "tPath=&action=xxx&pid=37&value=13&fname=aaaa&fone=4321122"

Why does this jQuery code not work?

Why doesn't the following jQuery code work?
$(function() {
var regex = /\?fb=[0-9]+/g;
var input = window.location.href;
var scrape = input.match(regex); // returns ?fb=4
var numeral = /\?fb=/g;
scrape.replace(numeral,'');
alert(scrape); // Should alert the number?
});
Basically I have a link like this:
http://foo.com/?fb=4
How do I first locate the ?fb=4 and then retrieve the number only?
Consider using the following code instead:
$(function() {
var matches = window.location.href.match(/\?fb=([0-9]+)/i);
if (matches) {
var number = matches[1];
alert(number); // will alert 4!
}
});
Test an example of it here: http://jsfiddle.net/GLAXS/
The regular expression is only slightly modified from what you provided. The global flag was removed, as you're not going to have multiple fb='s to match (otherwise your URL will be invalid!). The case insensitive flag flag was added to match FB= as well as fb=.
The number is wrapped in curly brackets to denote a capturing group which is the magic which allows us to use match.
If match matches the regular expression we specify, it'll return the matched string in the first array element. The remaining elements contain the value of each capturing group we define.
In our running example, the string "?fb=4" is matched and so is the first value of the returned array. The only capturing group we have defined is the number matcher; which is why 4 is contained in the second element.
If you all you need is to grab the value of fb, just use capturing parenthesis:
var regex = /\?fb=([0-9]+)/g;
var input = window.location.href;
var tokens = regex.exec(input);
if (tokens) { // there's a match
alert(tokens[1]); // grab first captured token
}
So, you want to feed a querystring and then get its value based on parameters?
I had had half a mind to offer Get query string values in JavaScript.
But then I saw a small kid abusing a much respectful Stack Overflow answer.
// Revised, cooler.
function getParameterByName(name) {
var match = RegExp('[?&]' + name + '=([^&]*)')
.exec(window.location.search);
return match ?
decodeURIComponent(match[1].replace(/\+/g, ' '))
: null;
}
And while you are at it, just call the function like this.
getParameterByName("fb")
How about using the following function to read the query string parameter in JavaScript:
function getQuerystring(key, default_) {
if (default_==null)
default_="";
key = key.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");
var regex = new RegExp("[\\?&]"+key+"=([^&#]*)");
var qs = regex.exec(window.location.href);
if(qs == null)
return default_;
else
return qs[1];
}
and then:
alert(getQuerystring('fb'));
If you are new to Regex, why not try Program that illustrates the ins and outs of Regular Expressions

How to know if JavaScript string.replace() did anything?

The replace function returns the new string with the replaces, but if there weren't any words to replace, then the original string is returned. Is there a way to know whether it actually replaced anything apart from comparing the result with the original string?
A simple option is to check for matches before you replace:
var regex = /i/g;
var newStr = str;
var replaced = str.search(regex) >= 0;
if(replaced){
newStr = newStr.replace(regex, '!');
}
If you don't want that either, you can abuse the replace callback to achieve that in a single pass:
var replaced = false;
var newStr = str.replace(/i/g, function(token){replaced = true; return '!';});
As a workaround you can implement your own callback function that will set a flag and do the replacement. The replacement argument of replace can accept functions.
Comparing the before and after strings is the easiest way to check if it did anything, there's no intrinsic support in String.replace().
[contrived example of how '==' might fail deleted because it was wrong]
Javascript replace is defected by design. Why? It has no compatibility with string replacement in callback.
For example:
"ab".replace(/(a)(b)/, "$1$2")
> "ab"
We want to verify that replace is done in single pass. I was imagine something like:
"ab".replace(/(a)(b)/, "$1$2", function replacing() { console.log('ok'); })
> "ab"
Real variant:
"ab".replace(/(a)(b)/, function replacing() {
console.log('ok');
return "$1$2";
})
> ok
> "$1$2"
But function replacing is designed to receive $0, $1, $2, offset, string and we have to fight with replacement "$1$2". The solution is:
"ab".replace(/(a)(b)/, function replacing() {
console.log('ok');
// arguments are $0, $1, ..., offset, string
return Array.from(arguments).slice(1, -2)
.reduce(function (pattern, match, index) {
// '$1' from strings like '$11 $12' shouldn't be replaced.
return pattern.replace(
new RegExp("\\$" + (index + 1) + "(?=[^\\d]|$)", "g"),
match
);
}, "$1$2");
});
> ok
> "ab"
This solution is not perfect. String replacement itself has its own WATs. For example:
"a".replace(/(a)/, "$01")
> "a"
"a".replace(/(a)/, "$001")
> "$001"
If you want to care about compatibility you have to read spec and implement all its craziness.
If your replace has a different length from the searched text, you can check the length of the string before and after. I know, this is a partial response, valid only on a subset of the problem.
OR
You can do a search. If the search is successfull you do a replace on the substring starting with the found index and then recompose the string. This could be slower because you are generating 3 strings instead of 2.
var test = "Hellllo";
var index = test.search(/ll/);
if (index >= 0) {
test = test.substr(0, index - 1) + test.substr(index).replace(/ll/g, "tt");
}
alert(test);
While this will require multiple operations, using .test() may suffice:
const regex = /foo/;
const yourString = 'foo bar';
if (regex.test(yourString)) {
console.log('yourString contains regex');
// Go ahead and do whatever else you'd like.
}
The test() method executes a search for a match between a regular expression and a specified string. Returns true or false.
With indexOf you can check wether a string contains another string.
Seems like you might want to use that.
have a look at string.match() or string.search()
After doing any RegExp method, read RegExp.lastMatch property:
/^$/.test(''); //Clear RegExp.lastMatch first, Its value will be ''
'abcd'.replace(/bc/,'12');
if(RegExp.lastMatch !== '')
console.log('has been replaced');
else
console.log('not replaced');

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