How to use a regular expression within jQuery's .match()

Question

I have been trying to get a couple similar regular expressions to work within a jQuery script that is using the .match() function.

The old version of the RegEx I was using worked but since 'upgrading it' to be more restrictive I now cannot get it to run successfully:

I am using this RegEx:

var termString = queryString.match('/(?<=' + queryTermIdentifier + ').*?(?=\+)+/g');

But it is producing this error:

Uncaught SyntaxError: Invalid regular expression: //(?<=term=).*?(?=+)+/g/: Nothing to repeat
    at String.match (<anonymous>)
    at ready-functions.js?200323021240:1361
    at ready-functions.js?200323021240:1575
    at ready-functions.js?200323021240:1624

Where lines 1361 is where the RegEx is used. Line 1575 is the end of the function which uses it. The last incident on 1624 is the end of the document and self-executing jQuery function.

I am using a couple of these and they are all pretty similar:

var termString = queryString.match('/(?<=' + queryTermIdentifier + ').*?(?=\+)+/g');
var categoryString = queryString.match('/(?<=' + queryCategoryIdentifier + ').*?(?=\+)+/g');
var tagString = queryString.match('/(?<=' + queryTagIdentifier + ').*?(?=$)+/g');

They are all variations on a look-back '?<=' for a string up until an instance of a '+' for the first two or the end of the line in the last one.

As the console outputs two '/'s I tried removing this, and it brings it down to one '/'. I have also tried escaping it and that also works.

Not to sure how to proceed as this works within the RegExr tool I used to write it: regexr.com/50trq

Edit (Second Attempt)

var queryString = window.location.search;

var queryTermString = '';
var queryCategoryString = '';
var queryTagString = '';

var queryTermIdentifier = 'term=';
var queryCategoryIdentifier = 'category=';
var queryTagIdentifier = 'tag=';

if (queryString.indexOf(queryTermIdentifier)) {
    console.log(queryTermIdentifier + 'was found');
    var myReg = new RegExp('(?<=' + queryTermIdentifier + ').*?(?=\+)', 'g');
    var termStringArray = myReg.exec(queryString);
    if (termStringArray.length) {
        queryTermString = termStringArray.index;
    }
}

I am trying this method, however I still receive the same error.

Edit 2

(Swap 'term' for 'phrase' add additional '\' to '+' so is '\+').

I have removed the term 'term' as this I think is reserved for some sort of WordPress functionality, so have replaced it with 'phrase'.

I have also added an additional '\' to the usage of '+' as requested.

Here is the updated relevant snippet:

var queryString = window.location.search;
console.log(queryString);
// This returns '?phrase=hello+category=world+tag=youokay'

if (queryString.length) {
    var queryTermString = '';

    var queryTermIdentifier = 'phrase=';

    if (queryString.indexOf(queryTermIdentifier) > 0) {
        console.log(queryTermIdentifier + 'was found in query string');

        var myTermReg = new RegExp('/(?<=' + queryTermIdentifier + ').*?(?=&)', 'g');
        var termStringArray = myTermReg.exec(queryString);
        console.log(termStringArray);
        // THIS IS ALWAYS NULL???
        if (termStringArray.length > 0) {
            queryTermString = termStringArray.index;
        }
    }
}

This seems to have allowed the code to execute an extra line or two. However, now the console returns

Uncaught TypeError: Cannot read property 'length' of null

Referencing the line:

if (termStringArray.length) {

I can't comprehend why this is the case.

You must use the `RegExp` constructor to build a regex dynamically using variables. — Wiktor Stribiżew, Mar 23 '20 at 09:47
If I remove the use of the variables and use a static value within the match() is returns the same error. Please can you provide further guidance? — Jason Is My Name, Mar 23 '20 at 09:53
Yes, see another dupe: http://stackoverflow.com/questions/7427731/why-this-javascript-regex-doesnt-work. The regex must be `/abc/g`, and not `'/abc/g'` — Wiktor Stribiżew, Mar 23 '20 at 09:54
I think I understand, however I still cannot get it to work, please see my edit. — Jason Is My Name, Mar 23 '20 at 10:10
`').*?(?=\+)'` must be `').*?(?=\\+)'`, see https://stackoverflow.com/questions/17863066/why-do-regex-constructors-need-to-be-double-escaped — Wiktor Stribiżew, Mar 23 '20 at 10:11
I have tried this and tried my best to read up and debunk it, please may you take a look at my latest edit? — Jason Is My Name, Mar 23 '20 at 11:39
I realise the indexOf of course will be TRUE as it is -1. Which of course is not 0. Therefore TRUE. — Jason Is My Name, Mar 23 '20 at 11:45
`/` are regex delimiters used in *regex literals*. You are using a RegExp constructor, hence, replace `'/(?<=' ` with `'(?<=' ` — Wiktor Stribiżew, Mar 23 '20 at 11:47
Just the trick, thank you for your continued support! If you would like to write up your comments as an answer, I would be happy to accept. If you enjoyed helping and found my question was phrased well, please upvote. Good day sir! — Jason Is My Name, Mar 23 '20 at 12:27

How to use a regular expression within jQuery's .match()

Edit (Second Attempt)

Edit 2

0 Answers0