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 Methods
Regular Expression Search and Replace can be done with different methods.
These are the most common:
String Methods
| Method | Description |
|---|---|
| match() | Returns an Array of results |
| matchAll() | Returns an Iterator of results |
| replace() | Returns a new String |
| replaceAll() | Returns a new String |
| search() | Returns the index of the first match |
| split() | Returns an Array of results |
RegExp Methods
| Method | Description |
|---|---|
| exec() | Returns an Iterator of results |
| test() | Returns 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 |
