function _javascript techniques for retrieving element indexes in JavaScript

This is the problem I found when I wrote the structure/performance/behavior completely separate tab (JQ version and native JS version). Today, a friend asked me this question, this function is indeed very practical. Share with you my approach to implementation.
Code:

Copy Code code as follows:

function index (current, obj) {
for (var i = 0; i < obj.length; i++) {
if (obj[i] = = current) {
return i;
}
}
}

Principle:
By iterating through a for loop to find the element that is equal to the current element in the current collection, the subscript value of the element is the index value of the current element in the element collection.

Optimized under:

Copy Code code as follows:

function index (current, obj) {
for (var i = 0, length = obj.length i<length; i++) {
if (obj[i] = = current) {
return i;
}
}
}