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Array.lastIndexOf()ECMAScript 5

search backward through an array


array.lastIndexOf(value) array.lastIndexOf(value, start)


value The value to search array for.


An optional array index at which to begin the search. If omitted, the search begins with the last element of the array.


The highest index <= start of array at which the element is === to value, or -1 if no such matching element exists.


This method searches backward through successively lower elements of array for an element that is equal to value, and returns the index of the first such element it finds. If start is specified, it is used as the starting position for the search; otherwise the search begins at the end of the array. The ===operator is used to test equality. The return value is the index of the first matching element found, or -1 if no match is found.

See Also

Array.indexOf() , String.lastIndexOf()


the size of an array



Core JavaScript Reference | 729


The length property of an array is always one larger than the index of the highest element defined in the array. For traditional “dense” arrays that have contiguous elements and begin with element 0, the length property specifies the number of elements in the array.

The length property of an array is initialized when the array is created with the Array() constructor method. Adding new elements to an array updates the length, if necessary:

a = new Array(); // a.length initialized to 0

b = new Array(10); // b.length initialized to 10

c = new Array("one", "two", "three"); // c.length initialized to 3

c[3] = "four"; // c.length updated to 4

c[10] = "blastoff"; // c.length becomes 11

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