How to get the element second index in an array in javascript -

i have array follows

var arr = [10,12,34,23,12,89,34,12]; 

in have 12 3 times .i want find second index of 12 in javascript.is possible find.i tried lastindexof() .but did not me.is there way find this.

thanks in advance...

one more possible solution:

array.prototype.nthindexof = function(e, n) {     var index = -1;     (var = 0, len = this.length; < len; i++) {         if (i in && e === this[i] && !--n) {             index = i;             break;         }     }     return index; };  [10, 12, 34, 23, 12, 89, 34, 12].nthindexof(12, 2); // >> 4