Array.prototype.indexOf()

The indexOf() method of Array instances returns the first index at which a given element can be found in the array, or -1 if it is not present.

The indexOf() method compares searchElement to elements of the array using strict equality (the same algorithm used by the === operator). NaN values are never compared as equal, so indexOf() always returns -1 when searchElement is NaN.

The indexOf() method skips empty slots in sparse arrays.

The indexOf() method is generic. It only expects the this value to have a length property and integer-keyed properties.

Return value: The first index of searchElement in the array; -1 if not found.

Syntax example: indexOf(searchElement)