JavaScript String lastIndexOf()

The JavaScript String lastIndexOf() method returns the last index of occurance of a given value in the string, or -1 if it is not present.

The syntax of the lastIndexOf() method is:

str.lastIndexOf(searchValue, fromIndex)

Here, str is a string.


lastIndexOf() Parameters

The lastIndexOf() method takes in:

  • searchValue - The value to search for in the string. If no string is provided explicitly, fromIndex is returned.
  • fromIndex (optional) - The index to start searching the string backwards. By default it is +Infinity.

Notes:

  • If fromIndex >= string.length, the whole string is searched.
  • If fromIndex < 0, it is considered to be the same as 0.

Return value from lastIndexOf()

  • Returns the last index of the value in the string if it is present at least once.
  • Returns -1 if the value is not found in the string.

Note: The lastIndexOf() method is case sensitive.


Example: Using lastIndexOf() method

var str = "JavaScript is the world's most misunderstood programming language.";

// lastIndexOf() returns the last occurance
var index1 = str.lastIndexOf("language");
console.log(index1); // 57

var index2 = str.lastIndexOf("p");
console.log(index2); // 45

// second argument specifies the search's start index
var index3 = str.lastIndexOf("p", 44);
console.log(index3); // 8

// lastIndexOf returns -1 if not found
var index4 = str.lastIndexOf("Python");
console.log(index4); // -1

Output

57
45
8
-1

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