Javascript object functions not working

Question

I'm not really sure why my code isn't running correctly.. what I'm trying to do is create a grocery list object that has a couple of functions to add and remove items.. I can instantiate the objects with new items but my functions don't seem to work for some reason. If you could save me the few hairs left in my head and tell me where the issue is I would greatly appreciate it.

            var groceryList = function(itemNames,quantity) {
                if (Array.isArray(itemNames)) {
                    this.items = itemNames;
                    this.quantity = quantity

                    this.addItems = function(newItems){
                        if ( Array.isArray(newItems) ) {
                            this.items.concat(newItems);
                        }   else {
                            console.log("Please enter the items in an array fashion!");
                        };
                    };

                    this.removeItem = function(name) {
                        var listSize = this.items.length;
                        for (var i = 0; i < listSize; i++) {
                            if (this.items[i] == name) {
                                this.items.splice(i,1);
                                break;
                            } else {
                            console.log("Please enter the items in an array fashion!")
                            };
                        };
                    };
                } else {
                    console.log("Please enter the items in an array fashion!")
                };
            };

possible duplicate of "concat" does not join JavaScript arrays together? — Qantas 94 Heavy
– Qantas 94 Heavy, Commented Oct 19, 2014 at 5:55
This question is similar to: Why does array.concat(…) not modify the array?. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. — dumbass
– dumbass, Commented Dec 25, 2024 at 14:36

jfriend00 · Accepted Answer · 2014-10-19 02:13:37Z

1

.concat() returns a new array so you have to assign the result back to your instance variable.

So this:

this.items.concat(newItems);

needs to be changed to this:

this.items = this.items.concat(newItems);

or, you could actually use this to append to the array directly:

this.items.push.apply(this.items, newItems);

Because .push() can take more than one argument.

Then, in your .removeItem() function, you need to remove the item you actually found by changing this:

this.items.splice(2,1);

to this:

this.items.splice(i,1);

edited Oct 19, 2014 at 2:13

answered Oct 19, 2014 at 2:07

jfriend00

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2 Comments

Rudie Over a year ago

"Because .push() can take more than one argument." -- whaaaaaat! You learn something new every week!

WebAhmed Over a year ago

Thank you very much! I was trying to use concat() thinking it functioned similarly to push() but your explanation was pretty clear.

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