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regExp.test

The test() method executes a search for a match between a regular expression and a specified string. Returns true or false.

Syntax

regexObj.test(str)

Parameters

str
The string against which to match the regular expression.

Returns

true if there is a match between the regular expression and the string str. Otherwise, false.

Description

Use test() whenever you want to know whether a pattern is found in a string. test() returns a boolean, unlike the String.prototype.search() method (which returns the index of a match, or -1 if not found).

To get more information (but with slower execution), use the exec() method. (This is similar to the String.prototype.match() method.)

As with exec() (or in combination with it), test() called multiple times on the same global regular expression instance will advance past the previous match.

Examples

Using test()

Simple example that tests if "hello" is contained at the very beginning of a string, returning a boolean result.

const str = 'hello world!';
const result = /^hello/.test(str);

console.log(result); // true

The following example logs a message which depends on the success of the test:

function testInput(re, str) {
  let midstring;
  if (re.test(str)) {
    midstring = 'contains';
  } else {
    midstring = 'does not contain';
  }
  console.log(`${str} ${midstring} ${re.source}`);
}

Using test() on a regex with the "global" flag

When a regex has the global flag set, test() will advance the lastIndex of the regex. (RegExp.prototype.exec() also advances the lastIndex property.)

Further calls to test(str) will resume searching str starting from lastIndex. The lastIndex property will continue to increase each time test() returns true.

Note: As long as test() returns true, lastIndex will not reset—even when testing a different string!

When test() returns false, the calling regex's lastIndex property will reset to 0.

The following example demonstrates this behaviour:

const regex = /foo/g; // the "global" flag is set

// regex.lastIndex is at 0
regex.test('foo')     // true

// regex.lastIndex is now at 3
regex.test('foo')     // false

// regex.lastIndex is at 0
regex.test('barfoo')  // true

// regex.lastIndex is at 6
regex.test('foobar')  //false

// regex.lastIndex is at 0
// (...and so on)

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
test 1 12 1 4 5 1
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
test 1 18 4 10.1 1 1.0
Server
Node.js
test 0.1.100

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/test