string.substring

The substring() method returns the part of the string between the start and end indexes, or to the end of the string.

Syntax

str.substring(indexStart[, indexEnd])

Parameters

indexStart

The index of the first character to include in the returned substring.

indexEnd

Optional. The index of the first character to exclude from the returned substring.

Return value

A new string containing the specified part of the given string.

Description

substring() extracts characters from indexStart up to but not including indexEnd. In particular:

• If indexEnd is omitted, substring() extracts characters to the end of the string.
• If indexStart is equal to indexEnd, substring() returns an empty string.
• If indexStart is greater than indexEnd, then the effect of substring() is as if the two arguments were swapped; See example below.

Any argument value that is less than 0 or greater than stringName.length is treated as if it were 0 and stringName.length respectively. Any argument value that is NaN is treated as if it were 0.

Examples

Using substring()

The following example uses substring() to display characters from the string 'Mozilla':

var anyString = 'Mozilla';

// Displays 'M'
console.log(anyString.substring(0, 1));
console.log(anyString.substring(1, 0));

// Displays 'Mozill'
console.log(anyString.substring(0, 6));

// Displays 'lla'
console.log(anyString.substring(4));
console.log(anyString.substring(4, 7));
console.log(anyString.substring(7, 4));

// Displays 'Mozilla'
console.log(anyString.substring(0, 7));
console.log(anyString.substring(0, 10));

Using substring() with length property

The following example uses the substring() method and length property to extract the last characters of a particular string. This method may be easier to remember, given that you don't need to know the starting and ending indices as you would in the above examples.

// Displays 'illa' the last 4 characters
var anyString = 'Mozilla';
var anyString4 = anyString.substring(anyString.length - 4);
console.log(anyString4);

// Displays 'zilla' the last 5 characters
var anyString = 'Mozilla';
var anyString5 = anyString.substring(anyString.length - 5);
console.log(anyString5);

Difference between substring() and substr()

There's a subtle difference between the substring() and substr() methods, and you should be careful not get them confused.

The arguments of substring() represent the starting and ending indexes, while the arguments of substr() represent the starting index and the length of characters to include in the returned string.

var text = 'Mozilla';
console.log(text.substring(2,5)); // => "zil"
console.log(text.substr(2,3)); // => "zil"

Replacing a substring within a string

The following example replaces a substring within a string. It will replace both individual characters and substrings. The function call at the end of the example changes the string 'Brave New World' to 'Brave New Web'.

// Replaces oldS with newS in the string fullS
function replaceString(oldS, newS, fullS) {
  for (var i = 0; i < fullS.length; ++i) {
    if (fullS.substring(i, i + oldS.length) == oldS) {
      fullS = fullS.substring(0, i) + newS + fullS.substring(i + oldS.length, fullS.length);
    }
  }
  return fullS;
}

replaceString('World', 'Web', 'Brave New World');

Note that this can result in an infinite loop if oldS is itself a substring of newS — for example, if you attempted to replace 'World' with 'OtherWorld' here. A better method for replacing strings is as follows:

function replaceString(oldS, newS, fullS) {
  return fullS.split(oldS).join(newS);
}

The code above serves as an example for substring operations. If you need to replace substrings, most of the time you will want to use String.prototype.replace().

Specifications

Browser compatibilityUpdate compatibility data on GitHub

See also

• String.prototype.substr()
• String.prototype.slice()