RegExp Lookahead x(?=y)
Example
let text = "W3Schools Tutorials";
let pattern = /W3Schools(?= Tutorials)/;
let result = pattern.test(text);
Try it Yourself »
Description
/x(?=y)/ matches "x" only if "x" is followed by "y".
Syntax
new RegExp("x(?=y)")
or simply:
/x(?=y)/
Regular Expression Search Methods
In JavaScript, a regular expression text search, can be done with different methods.
With a pattern as a regular expression, these are the most common methods:
String Methods
| match(pattern) | An Array of results |
| matchAll(pattern) | An Iterator of results |
| replace(pattern, rep) | A new String |
| search(pattern) | Index of the first match |
| split(pattern) | An Array of results |
RegExp Methods
| pattern.exec() | An Iterator of results |
| pattern.test() | true or false |
Browser Support
/x(?=y)/ is an ECMAScript1 (JavaScript 1997) feature.
It is supported in all browsers:
| Chrome | Edge | Firefox | Safari | Opera | IE |
| Yes | Yes | Yes | Yes | Yes | Yes |
