Question

57

Does Javascript have an enhanced for loop syntax similar to Java's

rated 0 times [ 62] [ 5] / answers: 1 / hits: 69496 / 13 Years ago, fri, december 30, 2011, 12:00:00

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]);

}

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3 Years ago

answered 13 Years ago dominics · Accepted Answer

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).