RegExp.prototype.test()
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
The test() method of RegExp instances executes a search with this regular expression for a match between a regular expression and a specified string. Returns true if there is a match; false otherwise.
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. Using this
internally, test() can be used to iterate over multiple matches in a string
of text (with capture groups).
Try it
const str = "table football";
const regex = /fo+/;
const globalRegex = /fo+/g;
console.log(regex.test(str));
// Expected output: true
console.log(globalRegex.lastIndex);
// Expected output: 0
console.log(globalRegex.test(str));
// Expected output: true
console.log(globalRegex.lastIndex);
// Expected output: 9
console.log(globalRegex.test(str));
// Expected output: false
Syntax
test(str)
Parameters
str-
The string against which to match the regular expression. All values are coerced to strings, so omitting it or passing
undefinedcausestest()to search for the string"undefined", which is rarely what you want.
Return value
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()
This example 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) {
const midString = re.test(str) ? "contains" : "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 behavior:
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
regex.test("foobarfoo"); // true
// regex.lastIndex is at 3
regex.test("foobarfoo"); // true
// regex.lastIndex is at 9
regex.test("foobarfoo"); // false
// regex.lastIndex is at 0
// (...and so on)
Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-regexp.prototype.test |
Browser compatibility
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See also
- Regular expressions guide
RegExp