The test()
method executes a search for a match between a regular expression and a specified string. Returns true
or false
.
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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
Specification |
---|
ECMAScript (ECMA-262) The definition of 'RegExp.test' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
test | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Legend
- Full support
- Full support
See also
- Regular Expressions chapter in the JavaScript Guide
RegExp
RegExp.prototype