push only unique elements in an array

Question

I have array object(x) that stores json (key,value) objects. I need to make sure that x only takes json object with unique key. Below, example \'id\' is the key, so i don\'t

Answer 1

JS objects are great tools to use for tracking unique items. If you start with an empty object, you can incrementally add keys/values. If the object already has a key for a given item, you can set it to some known value that is use used to indicate a non-unique item.

You could then loop over the object and push the unique items to an array.

var itemsObj = {};
var itemsList = [];
x = [{"id":"item1","val":"foo"},
    {"id":"item2","val":"bar"},
    {"id":"item1","val":"baz"},
    {"id":"item1","val":"bez"}];

for (var i = 0; i < x.length; i++) {
    var item = x[i];
    if (itemsObj[item.id]) {
        itemsObj[item.id] = "dupe";
    }
    else {
        itemsObj[item.id] = item;
    }
}

for (var myKey in itemsObj) {
    if (itemsObj[myKey] !== "dupe") {
        itemsList.push(itemsObj[myKey]);
    }
}

console.log(itemsList);

See a working example here: https://jsbin.com/qucuso

If you want a list of items that contain only the first instance of an id, you can do this:

var itemsObj = {};
var itemsList = [];
x = [{"id":"item1","val":"foo"},
    {"id":"item2","val":"bar"},
    {"id":"item1","val":"baz"},
    {"id":"item1","val":"bez"}];

for (var i = 0; i < x.length; i++) {
    var item = x[i];
    if (!itemsObj[item.id]) {
        itemsObj[item.id] = item;
        itemsList.push(item);
    }
}

console.log(itemsList);