How to add object only if it does not exist in list using javascript?

JSON.stringify(obj1) === JSON.stringify(obj2);

You can compare the objects with the above code but there's alittle trick in this.It results in true if both objects are like {x: 100, y: 1} and {x: 100, y: 1} but shows false if {x: 100, y: 1} and {y: 1, x: 100}.

You can use a comparator

    var testList = [];

    var myComparator = function (obj1, obj2) {
      // check if they are the same
      return obj1.keya === obj2.keya && obj1.keyb === obj2.keyb;  
    };

    var addIfNotInList = function(obj, list, comparator) {
        // you can also declare the comparing function here as default
        comparator = comparator || myComparator;

        // check if already in the list
        var exists = list.some(function(listItem) {
            return comparator(obj, listItem);
        });

        if(!exists) {
            list.push(obj);
        }
    };

    addIfNotInList({'keya':'a','keyb':'b'}, testList);
    addIfNotInList({'keya':'a5','keyb':'b2'}, testList);
    addIfNotInList({'keya':'a','keyb':'b'}, testList);

    console.log(testList);

You can also use underscore.js's utility functions for comparison: isEqual

I would use something like this, which loops through the array and checks each item against your argument. Each time it doesn't match counter increases, so if counter is as large as the array's length at the end, then the object must not match any that is already in there. Hope this helps!

var addIfNotInList = function(object, testList){

var counter = 0;

    for(var i = 0; i < testList.length, i++){

        if(testList[i]) !== object){

        counter++;

        }

    }

    if(counter === testList.length){

    testList.push(object)

    }

};

You should compare object equality by looping all elements in testList. if you use underscorejs, it is pretty easy.

function addIfNotInList(obj, list) {
    var doesNotExist = _.every(list, function(item) {
        return !_.isEqual(item, obj);
    });
    if (doesNotExist) {
        list.push(obj);
    }
}