RegExp.prototype[Symbol.search]()

{{JSRef}} 

The [Symbol.search]() method of {{jsxref("RegExp")}}  instances specifies how String.prototype.search should behave.

{{InteractiveExample("JavaScript Demo: RegExp.prototype[Symbol.search]()")}} 

class RegExp1 extends RegExp {
  constructor(str) {
    super(str);
    this.pattern = str;
  }
  [Symbol.search](str) {
    return str.indexOf(this.pattern);
  }
}

console.log("table football".search(new RegExp1("foo")));
// Expected output: 6

Syntax

regexp[Symbol.search](str)

Parameters

• str
  • : A {{jsxref("String")}}  that is a target of the search.

Return value

The index of the first match between the regular expression and the given string, or -1 if no match was found.

Description

This method is called internally in {{jsxref("String.prototype.search()")}} . For example, the following two examples return the same result.

"abc".search(/a/);

/a/[Symbol.search]("abc");

This method does not copy the regular expression, unlike [Symbol.split]() or [Symbol.matchAll](). However, unlike [Symbol.match]() or [Symbol.replace](), it will set lastIndex to 0 when execution starts and restore it to the previous value when it exits, therefore generally avoiding side effects. This means that the g flag has no effect with this method, and it always returns the first match in the string even when lastIndex is non-zero. This also means sticky regexps will always search strictly at the beginning of the string.

const re = /[abc]/g;
re.lastIndex = 2;
console.log("abc".search(re)); // 0

const re2 = /[bc]/y;
re2.lastIndex = 1;
console.log("abc".search(re2)); // -1
console.log("abc".match(re2)); // [ 'b' ]

[Symbol.search]() always calls the regex’s exec() method exactly once, and returns the index property of the result, or -1 if the result is null.

This method exists for customizing the search behavior in RegExp subclasses.

Examples

Direct call

This method can be used in almost the same way as {{jsxref("String.prototype.search()")}} , except for the different value of this and the different arguments order.

const re = /-/g;
const str = "2016-01-02";
const result = re[Symbol.search](str);
console.log(result); // 4

Using [Symbol.search]() in subclasses

Subclasses of {{jsxref("RegExp")}}  can override [Symbol.search]() method to modify the behavior.

class MyRegExp extends RegExp {
  constructor(str) {
    super(str);
    this.pattern = str;
  }
  [Symbol.search](str) {
    return str.indexOf(this.pattern);
  }
}

const re = new MyRegExp("a+b");
const str = "ab a+b";
const result = str.search(re); // String.prototype.search calls re[Symbol.search]().
console.log(result); // 3

Specifications

{{Specifications}} 

Browser compatibility

{{Compat}} 

See also

• Polyfill of RegExp.prototype[Symbol.search] in core-js
• {{jsxref("String.prototype.search()")}} 
• RegExp.prototype[Symbol.match]()
• RegExp.prototype[Symbol.matchAll]()
• RegExp.prototype[Symbol.replace]()
• RegExp.prototype[Symbol.split]()
• {{jsxref("RegExp.prototype.exec()")}} 
• {{jsxref("RegExp.prototype.test()")}} 
• {{jsxref("Symbol.search")}}