Check whether a string matches a regex in JS

Question

I want to use JavaScript (can be with jQuery) to do some client-side validation to check whether a string matches the regex:

^([a-z0-9]{5,})$

Ideally it would be an expression that returned true or false.

I'm a JavaScript newbie, does match() do what I need? It seems to check whether part of a string matches a regex, not the whole thing.

Do you want a complete match, or just whether the string _contains_ a matching substring? — Kerrek SB, Jul 06 '11 at 21:12

score 1544 · Accepted Answer · edited Aug 11 '19 at 13:51

1544

Use regex.test() if all you want is a boolean result:

console.log(/^([a-z0-9]{5,})$/.test('abc1')); // false

console.log(/^([a-z0-9]{5,})$/.test('abc12')); // true

console.log(/^([a-z0-9]{5,})$/.test('abc123')); // true

...and you could remove the () from your regexp since you've no need for a capture.

edited Aug 11 '19 at 13:51

Code Maniac

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answered Jul 06 '11 at 21:10

user113716

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What does the initial ^ in the regex does there? – PedroD Dec 01 '16 at 22:13
12

@PedroD ^ implies begining or starts with – Nagaraju Dec 07 '16 at 07:06
So how would you do the opposite? "doesn't start with..." – PedroD Dec 07 '16 at 08:11
@PedroD http://stackoverflow.com/questions/899422/regular-expression-for-a-string-that-does-not-start-with-a-sequence – JHH Dec 15 '16 at 11:26
3

@stackdave are you perhaps working with Java, rather than JavaScript? – sfarbota Dec 27 '17 at 23:48
What would I do if I wanted to do something with the groups? It gives an error if there is no match. In addition, it would be inefficient to first run test, then run match later. – Mike Smith May 20 '21 at 18:10

score 226 · Answer 2 · edited May 28 '18 at 11:57

226

Use test() method :

var term = "sample1";
var re = new RegExp("^([a-z0-9]{5,})$");
if (re.test(term)) {
    console.log("Valid");
} else {
    console.log("Invalid");
}

edited May 28 '18 at 11:57

KeaganFouche

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answered Feb 16 '15 at 06:25

Abhijeet Kasurde

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Note that the version with `RegExp` allows to inject variable values into the regex string. – Christophe Roussy Apr 04 '16 at 09:48
3

had to remove double quotes in `new RegExp("^([a-z0-9]{5,})$")` in order to make it work – Facundo Colombier Oct 17 '18 at 19:30

pmrotule · Answer 3 · 2017-06-09T05:14:07.420

126

You can use match() as well:

if (str.match(/^([a-z0-9]{5,})$/)) {
    alert("match!");
}

But test() seems to be faster as you can read here.

Important difference between match() and test():

match() works only with strings, but test() works also with integers.

12345.match(/^([a-z0-9]{5,})$/); // ERROR
/^([a-z0-9]{5,})$/.test(12345);  // true
/^([a-z0-9]{5,})$/.test(null);   // false

// Better watch out for undefined values
/^([a-z0-9]{5,})$/.test(undefined); // true

edited Jun 09 '17 at 05:14

answered Jun 19 '14 at 15:01

pmrotule

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The reason it works with a number is because the number is coerced into a string, because it's given as a parameter when it's expecting a string. I wouldn't rely on this behavior. It depends on your environment's implementation of test(). (match fails because numbers don't have a `match` member). I'd reccomend explicitly converting your number to a string if you want to use it with a regex (`String(123)` for example). – Bronzdragon Jan 20 '19 at 14:47
The match can be used here, but if you look at performance, `test` performs 30% better when we just want to validate a string to match the regex and not extract substrings from it. – Akansh Feb 26 '19 at 06:19
@pmrotule Yeah, but it should be mentioned before match description. – Akansh Feb 26 '19 at 10:54
The most significant difference between test and match (and matchAll) is that match does things like to return a list of all matching sub-strings, while test only checks if there are any. Check the regex methods in https://javascript.info/regexp-methods – Juan Lanus Jan 13 '20 at 20:49

score 61 · Answer 4 · edited Nov 11 '14 at 06:21

61

Use /youregexp/.test(yourString) if you only want to know whether your string matches the regexp.

edited Nov 11 '14 at 06:21

J0e3gan

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answered Jul 06 '11 at 21:11

user278064

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score 17 · Answer 5 · edited Sep 17 '21 at 12:49

17

let str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
let regexp = /[a-d]/gi;
console.log(str.match(regexp));

edited Sep 17 '21 at 12:49

dota2pro

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answered Mar 19 '18 at 04:11

Mike

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score 16 · Answer 6 · edited Apr 19 '22 at 20:59

16

Here's an example that looks for certain HTML tags so it's clear that /someregex/.test() returns a boolean:

if(/(span|h[0-6]|li|a)/i.test("h3")) alert('true');

Remember to indicate ^ for beginning of the string and $ for the end, if you want to test the exact match of entire string.

Example:

/[a-z]+/.test('aaa111'); // true
/^[a-z]+$/.test('aaa111'); // false

edited Apr 19 '22 at 20:59

Kostanos

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answered Sep 23 '13 at 15:35

user2449231

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score 9 · Answer 7 · edited Nov 07 '20 at 01:19

9

const regExpStr = "^([a-z0-9]{5,})$"
const result = new RegExp(regExpStr, 'g').test("Your string") // here I have used 'g' which means global search
console.log(result) // true if it matched, false if it doesn't

edited Nov 07 '20 at 01:19

Penny Liu

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answered Apr 30 '20 at 06:40

Geetanshu Gulati

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score 5 · Answer 8 · answered Apr 11 '19 at 20:37

5

try

 /^[a-z\d]{5,}$/.test(str)

console.log( /^[a-z\d]{5,}$/.test("abc123") );

console.log( /^[a-z\d]{5,}$/.test("ab12") );

answered Apr 11 '19 at 20:37

Kamil Kiełczewski

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What new value does this code-only answer bring to the page? – mickmackusa Jun 13 '19 at 23:53
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currently it is shortest solution (due to regexp simplification) – Kamil Kiełczewski Jun 14 '19 at 05:27

score 5 · Answer 9 · answered Apr 24 '19 at 22:41

I would recommend using the execute method which returns null if no match exists otherwise it returns a helpful object.

let case1 = /^([a-z0-9]{5,})$/.exec("abc1");
console.log(case1); //null

let case2 = /^([a-z0-9]{5,})$/.exec("pass3434");
console.log(case2); // ['pass3434', 'pass3434', index:0, input:'pass3434', groups: undefined]

score 5 · Answer 10 · answered Feb 07 '20 at 06:42

You can try this, it works for me.

 <input type="text"  onchange="CheckValidAmount(this.value)" name="amount" required>

 <script type="text/javascript">
    function CheckValidAmount(amount) {          
       var a = /^(?:\d{1,3}(?:,\d{3})*|\d+)(?:\.\d+)?$/;
       if(amount.match(a)){
           alert("matches");
       }else{
        alert("does not match"); 
       }
    }
</script>

score 3 · Answer 11 · answered Mar 18 '19 at 14:52

3

please try this flower:

/^[a-z0-9\_\.\-]{2,20}\@[a-z0-9\_\-]{2,20}\.[a-z]{2,9}$/.test('abc@abc.abc');

true

answered Mar 18 '19 at 14:52

Jaber Alshami

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Madhusoodan P · Answer 12 · 2022-04-07T02:33:03.510

0

If you don't want ^ and $ around the regex (I had such a usecase) you can do something like

let reg = /[a-zA-Z0-9]+/g
let txt = "hello"
let matches = reg.exec(txt)[0] == txt
console.log(`It ${matches ? "does" : "doesn't"} match`)

edited Apr 07 '22 at 02:33

answered Apr 07 '22 at 02:27

Madhusoodan P

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score 0 · Answer 13 · answered May 29 '22 at 07:17

Update/Add

If the query string does not present in the URL then the below solution will work to add the param in the URL, if it already exists then it will update.

function updateUrlParameter(url, param, value) {
  var regex = new RegExp("(?<=[?|&])(" + param + "=)[^&]+", "i");
  if (regex.test(url)) {
    return url.replace(regex, param + "=" + value);
  } else {
    if (window.location.search) {
      return `${url}&${param}=${value}`;
    }else{
      return `${url}?${param}=${value}`;
    }
  }
}

Check whether a string matches a regex in JS

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