Writing a function to add or modify an existing object inside an array

Question

I have an array of objects. Each object has two properties, id and quantity.

I wrote a function to add an object to the array. But the function must check if the object already exists within the array. If it does exist the function must increment the quantity property. Otherwise it must add a new object.

Is there an idiomatic way to achieve the same result? I feel that looping over the array to compare the id of the object at index against the id passed as argument is not the right approach.

I am also suspicious of the found = false temporary variable.

Finally, in Ruby we are encouraged to break down long methods into smaller ones. I am aware that JavaScript is not the same, but I feel that this could be further refactored.

addItem = function(id, items) { var found, i; found = false; i = 0; while (i < items.length) { if (id === items[i].id) { items[i].quantity++; found = true; break; } i++; } if (!found) { return items.push({ id: id, quantity: 1 }); } }; 

Answer 1

I also don't like the found variable, I think you should extract that part to a indexOf method to return the index of the item you want to change, as you only seem to want to do items[i].quantity++; once. This way you can return the index directly. I would also use a for loop rather than while, as you're looping through a fixed number of items.

indexOf = function(id, items) { var i = 0; var len = items.length; for (i = 0; i < len; i++) { if (id === items[i].id) { return i; } } return -1; } 

This way you can call your indexOf function from your addItem function and check if the return value is -1, if it is then you call items.push, if it's not -1 then you perform items[index].quantity++;.

Instead of using an array structure, you could use more of a Set structure, which can be implemented in JavaScript as seen in this StackOverflow question, assuming that your id can easily be converted to a string.

Answer 2

Why are you using an array to do the job of a map? Use the right data structures....

... instead, use a hashmap (associative array) of [id, quantity]. If id exists in hashmap, then increment up the value at hashmap[id].

Answer 3

I don't really like that found flag. Also using while or for loops ads a bit of extra code to write to get the value of an arrays items. I would use the filter method for this case.

addItem = function(id, items) { var foundItem = items.filter(function(item) { return item.id === id; })[0]; if (foundItem) { foundItem.quantity++; } else { //return the new length here cause that is what you did return items.push({ id: id, quantity: 1 }); } }; 

Answer 4

You don't need to use the found variable. Use return when done.

You can also use for instead of while.

addItem = function(id, items) { for (var i = 0; i < items.length; i++) { if (id === items[i].id) { items[i].quantity++; return; } } return items.push({ id: id, quantity: 1 }); };