Iterate over a collection of objects in javascript and return true from that function

Question

I have an object called collection, and I want to test to see if justin is part of this collection.

collection = { 0:{screen_name:"justin"},1:{screen_name:"barry"}}

I'm trying to discover the most efficient method, to pass in a name to function called present_user(user), to see if the user is part of the collection and I'm kind of stumped.

So my collection is built up of objects 0, 1, n+1. I'm trying to iterate through this collection. So far I only test [0]

function present_user(user) {
  collection[0]["screen_name"] == user -> return true in the case of "justin"
}

How can I iterate over all values of this collection, and return true if the user_name "justin" is passed into a function?

Answer 1

Your collection is an object and not an array, so this would be a way to do it:

var present_user = function(user){
    for (var k in collection) {
        if (collection[k]['screen_name'] == user) return true;
    }
    return false;
};

Answer 2

If your outer object keys are all numbers, you should be using an array instead:

var collection = [{screen_name:"justin"}, {screen_name:"barry"}];

Then iterate with:

function present_user(user) {
    for(var i=0; i < collection.length; i++) {
        if(collection[i].screen_name === user) return true;
    }
}

You could loop the object collection too (with for..in, see mVChr's answer), but in this case it looks like you really should be using an array.

Answer 3

You could also turn a collection or object into an array, so that you could use array methods to iterate:

Object.values(collectionOrObject);

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_objects/Object/values

This especially comes in handy when you use the native javascript dom selectors like:

document.getElementsByClassName('someClass');

Which returns a collection