JS: Array.prototype.indexOf

By Xah Lee. Date: . Last updated: .

myArray.indexOf(value)

myArray.indexOf(value, start_index)

Return the index of first element that is value. Search starts at index start_index (default to 0), from left to right.

Return -1 if not found.

1 argument example:

const rr = [3,4,5,6];
console.log ( rr.indexOf ( 5 ) ); // 2

2 arguments example:

const rr = ["b", 5, 6, "b"];
console.log ( rr.indexOf ( "b", 1 ) ); // 3

Reference

ECMAScript® 2016 Language Specification#sec-array.prototype.indexof

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