searchString

Substring to search for. All values arecoerced to strings, so omitting it or passingundefined causeslastIndexOf() to search for the string"undefined", which is rarely what you want.

positionOptional

The method returns the index of the last occurrence of the specified substring at a position less than or equal toposition, which defaults toInfinity. Ifposition is greater than the length of the calling string, the method searches the entire string. Ifposition is less than0, the behavior is the same as for0 — that is, the method looks for the specified substring only at index0.

• 'hello world hello'.lastIndexOf('world', 4) returns-1 — because, while the substringworld does occurs at index6, that position is not less than or equal to4.

• 'hello world hello'.lastIndexOf('hello', 99) returns12 — because the last occurrence ofhello at a position less than or equal to99 is at position12.

• 'hello world hello'.lastIndexOf('hello', 0) and'hello world hello'.lastIndexOf('hello', -5) both return0 — because both cause the method to only look forhello at index0.

The index of the last occurrence ofsearchString found, or-1 if not found.

Strings are zero-indexed: The index of a string's first character is0, and the index of a string's last character is the length of the string minus 1.

"canal".lastIndexOf("a"); // returns 3"canal".lastIndexOf("a", 2); // returns 1"canal".lastIndexOf("a", 0); // returns -1"canal".lastIndexOf("x"); // returns -1"canal".lastIndexOf("c", -5); // returns 0"canal".lastIndexOf("c", 0); // returns 0"canal".lastIndexOf(""); // returns 5"canal".lastIndexOf("", 2); // returns 2

ThelastIndexOf() method is case sensitive. For example, the followingexpression returns-1:

"Blue Whale, Killer Whale".lastIndexOf("blue"); // returns -1

The following example usesindexOf() andlastIndexOf() to locate values in the string"Brave, Brave New World".

const anyString = "Brave, Brave New World";console.log(anyString.indexOf("Brave")); // 0console.log(anyString.lastIndexOf("Brave")); // 7

• String.prototype.charAt()
• String.prototype.indexOf()
• String.prototype.split()
• Array.prototype.indexOf()
• Array.prototype.lastIndexOf()