Finding array element's position whitin the element itself in Javascript

Цhat is the most effective way to find an element position within an array, if we got access to the element itself?

var arr 开发者_开发百科= [];
for (var i = 0; i < 10; i++) {
    arr[i] = {test: Math.floor(Math.random() * 101)}
}
var test = arr[Math.floor(Math.random() * 11)];

Now how can I get the position of the element that test refer to?

I'd just store the position when generating it here, like this:

var arr = [];
for (var i = 0; i < 10; i++) {
    arr[i] = {test: Math.floor(Math.random() * 101)}
}
var index = Math.floor(Math.random() * 11);
var test = arr[index];
//index is the position

I assume that the random generation is just an example.

Now if you've got a reference to an element and want to find out its index you can use Array.indexOf method. It's a new feature so not all browsers support it natively, but it's easy to implement. A bare-bone solution would look like:

if (!Array.prototype.indexOf) {
  Array.prototype.indexOf = function (searchElement) {
    var len = this.length >>> 0;
    for (var i = 0; i < len; i++) {
      if (searchElement === this[i]) return i;
    }
    return -1;
  };
}

Now you can use it as:

index = array.indexOf(elem)    // index from an element reference
examp = [5,8,12,5].indexOf(12) // 2

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