javascript array.slice().push() not working as expected

Question

The following code produces (in Chrome javascript console)

a: (3) [1, 2, 3] b: (4) [1, 2, 3, 99] c: 4

I expected c to look like b. Why doesn't it?

function snafu(){
    var a = [1,2,3];
    var b = a.slice();
    var c = a.slice().push(99);
    b.push(99);
    console.log("a:",a,"  b:",b,"  c:",c);
}

you can replace push with concat and it should work

dubucha
– dubucha

2020-07-15 09:32:12 +00:00
Commented Jul 15, 2020 at 9:32 — dubucha
– dubucha, Commented Jul 15, 2020 at 9:32

user2575725 · Accepted Answer · 2018-04-25 10:57:40Z

2

Array.push() gives you value of Array.length and not array itself

var a = [];
var b = a.push(8); /* returns length of array after pushing value into array */
console.log('a = ', a, ', b = ', b);

answered Apr 25, 2018 at 10:57

user2575725

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Comments

M Shafique · Accepted Answer · 2018-04-25 11:34:26Z

1

Well, remember Array.slice() will return you new Array. So while pushing it on slice(), it'll return you length of the array.

function snafu(){
    var a = [1,2,3];
    var b = a.slice();
    var c = a.slice();
    c.push(99);
    b.push(99);
    console.log("a:",a,"  b:",b,"  c:",c);
}

snafu();

variable c will give you new Array so you can do whatever you want with c.

That's it. Easy!!!!

answered Apr 25, 2018 at 11:34

M Shafique

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