for of, for in or forEach?

for of loops are used for data structures that can be iterated over (iterables). Arrays and strings are examples of such structures. So if I have something like this:

let arr = [1, 2, 3, 4, 5]

for (let i of arr) console.log(i)

Would give me all the elements in that array.

for in on the other hand is used for objects, where I want to loop over an object literal.

let obj = { id: 1, name: 'abc }

for (let key in obj) console.log(key, obj[key])

Will list out the keys and corresponding values of the given object.

forEach is also used to loop over arrays but takes a function instead.

let arr = [1, 2, 3, 4, 5]

arr.forEach(number => console.log(number))

The advantage of for of would be that you can use keywords like break and continue to alter the flow which is not possible with forEach.

I personally use forEach loops wherever possible. The only time I will need to use a for loop will be if I need to break out of a loop early (e.g. I'm looping through until I find a specific element, and then stopping).

The for and for/in looping constructs give you access to the index in the array, not the actual element.

With forEach() and for/of, you get access to the array element itself.

Note:

• forEach keeps the variable’s scope to the block
• lower chance of accidental errors with forEach
• forEach is easier to read
• you can break out of a for loop earlier