Question

I need to determine if an object already exists in an array in javascript.

eg (dummycode):

var carBrands = [];

var car1 = {name:'ford'};
var car2 = {name:'lexus'};
var car3 = {name:'maserati'};
var car4 = {name:'ford'};

carBrands.push(car1);
carBrands.push(car2);
carBrands.push(car3);
carBrands.push(car4);

now the “carBrands” array contains all instances.
I’m now looking a fast solution to check if an instance of car1, car2, car3 or car4 is already in the carBrands array.

eg:

var contains =  carBrands.Contains(car1); //<--- returns bool.

car1 and car4 contain the same data but are different instances they should be tested as not equal.

Do I have add something like a hash to the objects on creation? Or is there a faster way to do this in Javascript.

I am looking for the fastest solution here, if dirty, so it has to be 😉 In my app it has to deal with around 10000 instances.

no jquery

Answer 1

Use something like this:

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

    return false;
}

In this case, containsObject(car4, carBrands) is true. Remove the carBrands.push(car4); call and it will return false instead. If you later expand to using objects to store these other car objects instead of using arrays, you could use something like this instead:

function containsObject(obj, list) {
    var x;
    for (x in list) {
        if (list.hasOwnProperty(x) && list[x] === obj) {
            return true;
        }
    }

    return false;
}

This approach will work for arrays too, but when used on arrays it will be a tad slower than the first option.