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JavaScript substr() Method: String Object

Description

The substr() method returns the characters in a string starting at a specified position and continuing for a specified number of characters.

Version

Implemented in JavaScript 1.0

Syntax

substr(start_pos, length])

Parameter

start_pos: Specifies the position in the string where to begin extracting characters.

length: Specifies the number of characters to extract.

Note:

  • start_pos is a character index. The index of the first character is 0, and the index of the last character is 1 less than the length of the string.
  • If start_pos is positive and greater than the length of the string, substr() returns no characters.
  • If start_pos is negative, substr() uses it as a character index from the end of the string.
  • If length is 0 or negative, substr() returns no characters.
  • If the length is not defined , start extracts characters to the end of the string.

Example:

The following web document demonstrates how the substr() method can be used in various ways.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="content-type" content="text/html; charset=iso-8859-1" />
<title>JavaScript String object - substr() method example</title>
</head>
<body>
<h1 style="color: red">JavaScript String object : substr() method</h1>
<hr />
<script type="text/javascript">
//This is done to make the following JavaScript code compatible to XHTML. <![CDATA[
var str = "abcdefghij"
document.write("Original string : "+str+"<br>")
document.write("(1,2) : ", str.substr(1,2)+"<br>")
document.write("(-2,2) : ", str.substr(-2,2)+"<br>")
document.write("(1) : ", str.substr(1)+"<br>")
document.write("(1,20) : ", str.substr(1,20)+"<br>")
document.write("(-20, 2) : ", str.substr(-20,2))
//]]>
</script>
</body>
</html>

View the example in the browser

Supported Browser

Internet Explorer 7 Firefox 3.6 Google Chrome 7 Safari 5.0.1 Opera 10
Yes Yes Yes Yes Yes

See also:

JavaScript Core objects, methods, properties.

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JavaScript: Tips of the Day

How to check whether a string contains a substring in JavaScript?

ECMAScript 6 introduced String.prototype.includes:

const string = "foo";
const substring = "oo";

console.log(string.includes(substring));

includes doesn't have Internet Explorer support, though. In ECMAScript 5 or older environments, use String.prototype.indexOf, which returns -1 when a substring cannot be found:

var string = "foo";
var substring = "oo";

console.log(string.indexOf(substring) !== -1);

Ref: https://bit.ly/3fFFgZv