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目录

JavaScript String indexOf()

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Examples

Search a string for "welcome":

let text = "Hello world, welcome to the universe.";
let result = text.indexOf("welcome");
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Search a string for "Welcome":

let text = "Hello world, welcome to the universe.";
let result = text.indexOf("Welcome");
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Find the first occurrence of "e":

let text = "Hello world, welcome to the universe.";
text.indexOf("e");
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Find the first occurrence of "e", starting at position 5:

let text = "Hello world, welcome to the universe.";
text.indexOf("e", 5);
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Find the first occurrence of "a":

let text = "Hello world, welcome to the universe.";
text.indexOf("a");
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Description

The indexOf() method returns the position of the first occurrence of a value in a string.

The indexOf() method returns -1 if the value is not found.

The indexOf() method is case sensitive.

See Also:

The lastIndexOf() Method

The search() Method

The match() Method

Syntax

string.indexOf( searchvalue, start)

Parameters

Parameter Description
searchvalue Required.
The string to search for.
start Optional.
The position to start from (default is 0).

Return Value

Type Description
A number The first position where the search-value occurs.
-1 if it never occurs.

The Differense Between
String indexOf() and String search()

The indexOf() method cannot search against a regular expression.

The search() cannot take a start position argument.

Related Pages

JavaScript Strings

JavaScript String Methods

JavaScript String Search

Browser Support

indexOf() is an ECMAScript1 (ES1) feature.

ES1 (JavaScript 1997) is fully supported in all browsers:

Chrome Edge Firefox Safari Opera IE
Yes Yes Yes Yes Yes Yes
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