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1

Is there an equivalent for ruby's array[n..m] in Javascript ?

For example:

>> a = ['a','b','c','d','e','f','g']
>> a[0..2]
=> ['a','b','c']

Thanks

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3  
yes, coffeescript! New-and-improved range, slice, splice and loop syntax. – Lance Pollard May 18 '11 at 23:02
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4 Answers

up vote 27 down vote accepted

Use the array.slice(begin [, end]) function.

var a = ['a','b','c','d','e','f','g'];
var sliced = a.slice(0, 3); //will contain ['a', 'b', 'c']

The last index is non-inclusive; to mimic ruby's behavior you have to increment the end value. So I guess slice behaves more like a[m...n] in ruby.

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up vote 4 down vote

a.slice(0, 3) Would be the equivalent of your function in your example.

https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/slice

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actually it would be a.slice(0, 3). slice in JavaScript doesn't included the end index. – Anurag Aug 26 '10 at 23:15
D'oh, nice catch, updated. – Robert Aug 26 '10 at 23:25
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up vote 1 down vote

Ruby and Javascript both have a slice method, but watch out that the second argument to slice in Ruby is the length, but in JavaScript it is the index of the last element:

var shortArray = array.slice(start, end);
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up vote 0 down vote

The second argument in slice is optional, too:

var fruits = ['apple','banana','peach','plum','pear'];
var slice1 = fruits.slice(1, 3);  //banana, peach, plum
var slice2 = fruits.slice(3);  //plum, pear

You can also pass a negative number, which selects from the end of the array:

var slice3 = fruits.slice(-3);  //peach, plum, pear

Here's the W3 Schools reference link.

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How about linking to Mozilla's javascript reference, which is far more informative and much better written than the W3 schools site (which has nothing to do with the W3C)? developer.mozilla.org/en/JavaScript/Reference/Global_Objects/… – Bobby Jack Aug 26 '10 at 23:50
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