Check whether a string matches a regex in JS

Question

I want to use JavaScript (I can also use jQuery) to do check whether a string matches the regex ^([a-z0-9]{5,})$, and get a true or false result.

match() seems to check whether part of a string matches a regex, not the whole thing. Does it solve the problem? Can I adapt it to solve the problem? How?

Answer 1

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.

Answer 2

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");
}

Answer 3

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

Answer 4

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

Answer 5

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

Answer 6

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

Answer 7

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

Answer 8

try

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

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

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

Answer 9

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]

Answer 10

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>

Answer 11

please try this flower:

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

true

Answer 12

Calling RegExp.prototype.test() is probably correct, but has a couple caveats:

• It will tell you whether a string "matches" a regex -- i.e. if it "contains a matching sequence" -- not whether the string is an "exact match".
• If a regex is global /g it actually stores state, from the MDN:

JavaScript RegExp objects are stateful when they have the global or sticky flags set (e.g., /foo/g or /foo/y). They store a lastIndex from the previous match... https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/test

This means, for the first point, you need to use anchors, where ^ indicates the start of a string, and $ indicates it's end. So a regex matching the full string "Cat" & nothing else would be: /^Cat$/

And secondly, you cannot reuse regex.test(str) with a global regex on the same string for this purpose, as it's meaning changes over time. E.g. (and note the failure, despite using different instances of string)

reg = /t/g;
console.log(reg.lastIndex); // 0 -- Never run
console.log(reg.test("Cat")); // true -- Matched "t"
console.log(reg.lastIndex); // 3 -- 3rd character was "t"
console.log(reg.test("Cat")); // false -- no more matches!

Answer 13

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`)

Answer 14

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}`;
    }
  }
}

Answer 15

match() seems to check whether part of a string matches a regex, not the whole thing. Does it solve the problem? Can I adapt it to solve the problem? How?

Yes, you can. ^ and $ are not needed if you so choose.

The idea is simple: .match() returns a "match" array. If the first element (i.e. the whole match, or $0) equals to the string, then we have a full match.

function fullMatch(string, regex) {
  const match = string.match(regex);
  return match?.[0] === string;
}

Try it:

console.config({ maximize: true });

function fullMatch(string, regex) {
  const match = string.match(regex);
  console.log(match);
  return match?.[0] === string;
}

const string = 'f00bar';
const testcases = [
  /\d+c?ba/, // false
  /f\d+\w+/, // true
  /[0a-z]+/g // false
];

testcases.forEach(
  regex => console.log(fullMatch(string, regex))
);

<script src="https://gh-canon.github.io/stack-snippet-console/console.min.js"></script>

Note that this does not work with g regexes, as this flag causes .match() to always return a normal array if there is at least one match.

You can, however, use RegExp#exec() instead:

function fullMatch(string, regex) {
  const match = regex.exec(regex);
  return match?.[0] === string;
}

Try it:

console.config({ maximize: true });

function fullMatch(string, regex) {
  const match = regex.exec(string);
  console.log(match);
  return match?.[0] === string;
}

const string = 'f00bar';
const testcases = [
  /\d+c?ba/, // false
  /f\d+\w+/, // true
  /[0a-z]+/g // true
];

testcases.forEach(
  regex => console.log(fullMatch(string, regex))
);

<script src="https://gh-canon.github.io/stack-snippet-console/console.min.js"></script>

One-liner:

const fullMatch = (string, array) => regex.exec(string)?.[0] === string;