If I do this:
a = []
b = [1, 2, 3]
a = b
a will then refer to b
I want to copy all of the values in b into a without changing any memory address/references.
-
There is no real guarantee that an object/array will retain its addressMedet Tleukabiluly– Medet Tleukabiluly2019-10-08 17:53:51 +00:00Commented Oct 8, 2019 at 17:53
Add a comment
|
4 Answers
You could push the values without changing the reference from a or b.
var a = [],
b = [1, 2, 3];
a.push(...b);
3 Comments
Medet Tleukabiluly
why not just
a = [...b]?
arizafar
also
Object.assign(a, b)
VLAZ
@MedetTleukabiluly that will create a new array. I think OP wants to change
a it in-place, although I'm not sure.If you want to populate a in-place, without ever discarding the initial array, then you can simply loop over b and add all the items in a:
var a = []
var b = [1, 2, 3]
var firstA = a; //get a initial element
b.forEach(function(item) {
this.push(item)
}, a);// <-- pass `a` as the `this` context
console.log("`a` is unchanged", a === firstA);
console.log("`a` is not `b`", a !== b);
console.log(a);2 Comments
Medet Tleukabiluly
what's the point in comparing
var firstA = a;, a === firstA ? it's always a referenceVLAZ
@MedetTleukabiluly to show that
a hasn't been reassigned. Superfluous, I know but it doesn't hurt.let a = b.map(x => x);
The .map() function will create a new array with values generated from the source elements via the passed-in callback function.
As noted in a comment
let a = b.slice();
is pretty much exactly the same.
Basically this saves you the step of
let a = [];
since one brand-new empty array is as good as another. However, if you really have your heart set on using the empty array explicitly initialized, you could use
b.forEach(x, i) { a[i] = x; });
2 Comments
Medet Tleukabiluly
why not just
a = b.slice()?
Pointy
@MedetTleukabiluly because I'm eating a very good sandwich and it's making me disoriented :)
A= b.slice(). It will create a shadow copy of element without changing original one. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice
