Question

I am wondering if JavaScript has an enhanced for loop syntax that allows you to iterate over arrays. For example, in Java, you can simply do the following:

String[] array = "hello there my friend".split(" ");

for (String s : array){
    System.out.println(s);
}

output is:

hello
there
my
friend

Is there a way to do this in JavaScript? Or do I have to use array.length and use standard for loop syntax as below?

var array = "hello there my friend".split(" ");

for (i=0;i<array.length;i++){
    document.write(array[i]);
}

Answer 1

JavaScript has a foreach-style loop (for (x in a)), but it is extremely bad coding practice to use it on an Array. Basically, the array.length approach is correct. There is also a a.forEach(fn) method in newer JavaScripts you can use, but it is not guaranteed to be present in all browsers – and it’s slower than the array.length way.

EDIT 2017: "We’ll see how it goes", indeed. In most engines now, .forEach() is now as fast or faster than for(;;), as long as the function is inline, i.e. arr.forEach(function() { ... }) is fast, foo = function() { ... }; arr.forEach(foo) might not be. One might think that the two should be identical, but the first is easier for the compiler to optimise than the second.

Belated EDIT 2020: There is now for (const item of iterable), which solves the downsides of using for (item in iterable).