⚖️for-of vs. forEach

JS⟩ syntax ⟩ for loops ⟩ for-of ⟩ vs. forEach

always use for-of in ES6.

It works on any iterable
It supports all kinds of control flow in the loop body, like continue, break, return, yield and await.

Don't use forEach. (In fact, never use forEach anywhere in ES6).

forEach has known pitfalls that make it unsuitable in some situations that can be properly handled with for or for-of:

callback function creates new context (can be addressed with arrow function)
doesn't support iterators
doesn't support generator yield and async..await
doesn't provide a proper way to terminate a loop early with break

👉 stackoverflow

let a = [];        // sparse array
a[1] = 'hi';
a[5] = 'world';

let forofCount = 0;
let foreachCount = 0;

// ⭐️ for-of: treats "holes" as `undefined`.
for (const value of a) {
    forofCount += 1;
    console.log(forofCount, value);
}
// 1 undefined, 2 'hi', 3 undefined, ... 6 'world'

// ⭐️ forEach: ignores "holes".
a.forEach(value => {
    foreachCount += 1;
    console.log(foreachCount, value);
})
// 1 'hi', 2 'world'

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Last updated 3 years ago