Array.protoype。每一个都比Array.prototype.forEach有什么劣势？

Question

Both methods iterate over the current array's elements but only Array.prototype.every allows you to break out of the loop similar to how you can use break to exit a for-loop.

When looking at browser compatibility matrixes both seem to be supported by the same browsers.

Are there any disadvantages (performance, readability, ...) to Array.prototype.every compared to forEach that I have missed or why isn't every more common?

Main main point here is that most of the times I want to use forEach as a replacement for the classic for-loop for the sake of readability, but given that there is no way to break out of a for-each loop, every appears to be more more an equivalent here. The option to use every for that has been mentioned on MDN .

Answer 1

They have very different purposes. While forEach executes a function with side effects (not very functional) for each element and returns nothing, every is a functional method to test whether all elements fulfill a given predicate and returns a boolean. Also, every does expect a callback that returns a boolean - which most forEach callbacks dont.

As an example:

> [1,2,3].forEach(console.log)
1
2
3
undefined
> [1,2,3].every(console.log)
1
false

If you want to use the iteration methods and need to break out, then yes you might abuse some / every , but that's not what they're made for. Notice that breaking the loop by returning a boolean does not lead to much better readability :-) I'd suggest to use them only when you can make use of the return value, ie if you need to know whether the loop aborted prematurely.

Answer 2

The purpose of every is to check if every element of an array meets a test - and it returns true of it is so. forEach just runs its argument for each element of the array. So in a sense if your function returns true, every and forEach are equivalent. But it is better to be explicit - if you want to test all elements, use every. If you want to execute a function for each element, use forEach.

Answer 3

From this exact question here: map, foreach and every

The difference is in the return values.

.map() returns a new Array of objects created by taking some action on the original item.

.every() returns a boolean - true if every element in this array satisfies the provided testing function. An important difference with .every() is that the test function may not always be called for every element in the array. Once the testing function returns false for any element, no more array elements are iterated. Therefore, the testing function should usually have no side effects .

.forEach() returns nothing - It iterates the Array performing a given action for each item in the Array.

Edit: Here's the MSDN Docs if you prefer.