如何获得数组/对象的长度

Question

Ok so I have a backbone model that is giving me the following array (or at least what I believe should be an array). Below is a screenshot of the console.log of my array.

So the array's name is myModel, and the following gives me an undefined value.

myModel.length

How can I go about getting the length of this array/Object so that I can loop over it?

Answer 1

What you have there could be an Array-like Object. The easiest thing to do is just to turn it into an Array. If you can use ES6 then your best option is Array.from(myModel) .

If you can't use ES6 you can use Array.prototype.slice.call(myModel) .

Both of these methods will turn your Array-like Object into an Array! (you do have to store the result in a variable)

Answer 2

It looks like you're working with an Object rather than an Array . In this case, I think your Object has keys 0 - 4, making it look like an array.

You can use the for... in approach to iterate through the Object in the way you would expect. Of course, you can also use getOwnPropertyNames et al if you're worried about the prototype chain, but your example is fine as it's just a simple object.

Answer 3

Well obviously that is just an object with array like properties such as;

var myModel = {0:"this", 1:"that"};

If you do;

var myArr = Array.from((myModel.length = Object.keys(myModel).length, myModel));

You will get a proper array like ["this", "that"] .