underscore.js _.lastIndexOf[Array]

Returns the index of the last occurrence of value in the array, or -1 if value is not present. Uses the native lastIndexOf function if possible

返回值在数组中最后出现的位置，如果没有出现，返回-1

_.lastIndexOf([1, 2, 3, 1, 2, 3], 2);
=> 4

源码:

 _.lastIndexOf = function(array, item) {
    if (array == null) return -1;
    if (nativeLastIndexOf && array.lastIndexOf === nativeLastIndexOf) return array.lastIndexOf(item);
    var i = array.length;
    while (i--) if (i in array && array[i] === item) return i;
    return -1;
  };