Array.prototype.indexOf()
The indexOf() method returns the first index at which a
given element can be found in the array, or -1 if it is not present.
Syntax
indexOf(searchElement)
indexOf(searchElement, fromIndex)
Parameters
searchElement- : Element to locate in the array.
fromIndexoptional- : Zero-based index at which to start searching, converted to an integer.
- Negative index counts back from the end of the array — if
fromIndex < 0,fromIndex + array.lengthis used. Note, the array is still searched from front to back in this case. - If
fromIndex < -array.lengthorfromIndexis omitted,0is used, causing the entire array to be searched. - If
fromIndex >= array.length, the array is not searched and-1is returned.
- Negative index counts back from the end of the array — if
- : Zero-based index at which to start searching, converted to an integer.
Return value
The first index of the element in the array; -1 if not found.
Description
The indexOf() method compares searchElement to elements of the array using strict equality (the same algorithm used by the === operator).
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.