JavaScript regex get number after string

Question

After coming to the shocking realization that regular expressions in JavaScript are somewhat different from the ones in PCE, I am stuck with the following.

In php I extract a number after x:

(?x)[0-9]+

In JavaScript the same regex doesn't work, due to invalid group resulting from the capturing parenthesis difference.

So I am trying to achieve the same trivial functionality, but I keep getting both the x and the number:

(?:x)([0-9]+)

How do I capture the number after x without including x?

(?!x)([0-9]+) = ([0-9]+). And (?x)[0-9]+ is also equal to [0-9]+. To get a sequence of digits after an x char in PHP/JS, you can just use /x(\d+)/ and grab Group 1 value. Or, use a lookbehind, /(?<=x)\d+/ — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jul 26, 2021 at 7:20

Jodevan · Accepted Answer · 2016-02-24 16:30:42Z

4

This works too:

/(?:x)([0-9]+)/.test('YOUR_STRING');

Then, the value you want is:

RegExp.$1 // group 1

answered Feb 24, 2016 at 16:30

Jodevan

7501 gold badge6 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Ælex Over a year ago

yes that sort of did what I was hoping for: var x = str.match(/(?:x)(\d+)/ to match the correct part, and then accessing it with x[1]. I'm sure there must be a more elegant way?

Jodevan Over a year ago

A more elegant way? Dude, I find this beautiful! :D

Jodevan Over a year ago

Seriously now, the way I wrote it is a very common way of using regex in Javascript.

Ælex Over a year ago

I was hoping that I wouldn't have to access an array but a single variable. This approach (which I thank you for) requires that I test the array length. Surely there is a way to do this with the regex? ATM it returns both x15 and then the second capture group 15.

jimplode · Accepted Answer · 2016-02-24 16:47:10Z

4

You can try the following regex: (?!x)[0-9]+

fiddle here: https://jsfiddle.net/xy6x938e/1/

This is assuming that you are now looking for an x followed by a number, it uses a capture group to capture just the numbers section.

var myString = "x12345";
var myRegexp = /x([0-9]+)/g;
var match = myRegexp.exec(myString);
var myString2 = "z12345";
var match2 = myRegexp.exec(myString2);

if(match != null && match.length > 1){
    alert('match1:' + match[1]);
}
else{
    alert('no match 1');
}
if(match2 != null && match2.length > 1){
    alert('match2:' + match2[1]);
}
else{
    alert('no match 2');
}

edited Feb 24, 2016 at 16:47

answered Feb 24, 2016 at 16:27

jimplode

3,5104 gold badges28 silver badges44 bronze badges

1 Comment

Ælex Over a year ago

actually this is wrong, it will match any number, ignoring whether its x, y or z

Wiktor Stribiżew · Accepted Answer · 2021-07-27 20:44:11Z

How do I capture the number after x without including x?

In fact, you just want to extract a sequence of digits after a fixed string/known pattern.

Your PCRE (PHP) regex, (?x)[0-9]+, is wrong becaue (?x) is an inline version of a PCRE_EXTENDED VERBOSE/COMMENTS flag (see "Pattern Modifiers"). It does not do anything meaningful in this case, (?x)[0-9]+ is equal to [0-9]+ or \d+.

You can use

console.log("x15 x25".match(/(?<=x)\d+/g));

You can also use a capturing group and then extract Group 1 value after a match is obtained:

const match = /x(\d+)/.exec("x15");
if (match) {
  console.log(match[1]); // Getting the first match
}

// All matches
const matches = Array.from("x15,x25".matchAll(/x(\d+)/g), x=>x[1]);
console.log(matches);

lino · Accepted Answer · 2016-02-24 16:34:31Z

2

(\d+) try this! i have tested on this tool with x12345 http://www.regular-expressions.info/javascriptexample.html

answered Feb 24, 2016 at 16:34

lino

1905 bronze badges

Comments

nilfalse · Accepted Answer · 2016-02-24 16:41:47Z

0

You still can use exclusive pattern (?!...)

So, for your example it will be /(?!x)[0-9]+/. Give a try to the following:

/(?!x)\d+/.exec('x123')
// => ["123"]

answered Feb 24, 2016 at 16:41

nilfalse

2,4292 gold badges20 silver badges17 bronze badges

1 Comment

Ælex Over a year ago

The problem with this regex (as commented at jimplode's post) is that it matches any number following a character, regardless if the key is x, y or z. See for yourself: regex101.com/r/oP2eR3/1

Collectives™ on Stack Overflow

JavaScript regex get number after string

5 Answers 5

4 Comments

1 Comment

Comments

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

4 Comments

1 Comment

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related