Copying an array in one line

Question

I want to create array, copy of an existing array, but not an instance of it. How i can do this in one line?

array1 = new Array('orange', 'red', 'blue', 'green');
array2 = new Array.apply(this, array1);

// Uncaught TypeError: function apply() is not a constructor

*"copy of an exist array but not instance of him"* What does that mean? — Felix Kling, Apr 10 '14 at 15:59
Please use your title to show the problem you're trying to solve. It's not the same as a subject line in a forum. The title should be something searchable. No one will ever search for "How can I do this?" In your case, you want to copy an existing array to a new array. — George Stocker, Apr 10 '14 at 16:00
@Derek朕會功夫: It's the problem he needs to have solved… — Bergi, Apr 10 '14 at 16:00

score 3 · Answer 1 · answered Apr 10 '14 at 15:58

Array.prototype.slice is the method you're looking for. You may also want to use a literal when defining your Array.

var array1, array2;

array1 = ['orange', 'red', 'blue', 'green'];
array2 = array1.slice();

Now have

array1.join() === array2.join(); // true
array1 === array2; // false

score 2 · Accepted Answer · edited May 23 '17 at 10:33

Omit the new to make apply work (otherwise it would be interpreted as new (Array.apply)(…)). Since the Array constructor doesn't require a new and can be called as a function as well, it would be as simple as:

array1 = new Array('orange', 'red', 'blue', 'green');
array2 = Array.apply(this, array1);

Related question: Use of .apply() with 'new' operator. Is this possible?

However, you shouldn't need to use the Array constructor at all, especially because it doesn't work well with single-numeric-element arrays. Better:

var array1 = ['orange', 'red', 'blue', 'green'];
var array2 = array1.slice();

+1 for at least including useful information that won't be found in most duplicates. — cookie monster, Apr 10 '14 at 16:05

score 1 · Answer 3 · answered Apr 10 '14 at 15:59

array2 = array1.slice(0);

Returns a new array containing all items from the source array starting from the index given in the argument, which in this case is zero so the whole array.

Note that if any of your array items are themselves objects (eg. multi-dimensional arrays) then the new array will still point to the same instance of those arrays:

array1 = [1,[2,3]];
array2 = array1.slice(0);
array2[0] = 4;
array2[1][0] = 5;

// array1 is now [1,[5,3]]!

score 0 · Answer 4 · answered Apr 10 '14 at 16:00

0

According to this article, you only need to do an array slice.

var array2 = array1.slice(0);

That article also covers deep cloning.

answered Apr 10 '14 at 16:00

Michael Lea Crawford

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2
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score 0 · Answer 5 · answered Apr 10 '14 at 16:01

0

Use array.slice

var copy = original.slice(0);

Copying an array in one line

5 Answers5