Cannot read property 'push' of undefined when combining arrays

Question

When pushing an array's contents to another array I get

"Uncaught TypeError: Cannot read property 'push' of undefined" error in this snippet.

var order = new Object(), stack = [];
for(var i=0;i<a.length;i++){
    if(parseInt(a[i].daysleft) == 0){ order[0].push(a[i]); }
    if(parseInt(a[i].daysleft) > 0){ order[1].push(a[i]); }
    if(parseInt(a[i].daysleft) < 0){ order[2].push(a[i]); }
}

Why do I get this error in the second if statement ? Thanks a lot!

Pointy · Accepted Answer · 2014-07-19T14:43:03.780

81

You get the error because order[1] is undefined.

That error message means that somewhere in your code, an attempt is being made to access a property with some name (here it's "push"), but instead of an object, the base for the reference is actually undefined. Thus, to find the problem, you'd look for code that refers to that property name ("push"), and see what's to the left of it. In this case, the code is

if(parseInt(a[i].daysleft) > 0){ order[1].push(a[i]); }

which means that the code expects order[1] to be an array. It is, however, not an array; it's undefined, so you get the error. Why is it undefined? Well, your code doesn't do anything to make it anything else, based on what's in your question.

Now, if you just want to place a[i] in a particular property of the object, then there's no need to call .push() at all:

var order = [], stack = [];
for(var i=0;i<a.length;i++){
    if(parseInt(a[i].daysleft) == 0){ order[0] = a[i]; }
    if(parseInt(a[i].daysleft) > 0){ order[1] = a[i]; }
    if(parseInt(a[i].daysleft) < 0){ order[2] = a[i]; }
}

edited Jul 19 '14 at 14:43

answered Jul 19 '14 at 14:36

Pointy

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if it's defined as an object.. shouldn't i be able to use any number in there? – d3nm4k Jul 19 '14 at 14:37
1

@d3nm4k no. You have to initialize `order[0]`, `order[1]`, and `order[2]` to have some value (an array I guess). That won't be done for you; why would it? – Pointy Jul 19 '14 at 14:40
1

OH, got it! I would've spend a lot more hours just for getting order[1] = []; out. Thank You! – d3nm4k Jul 19 '14 at 14:42
Thank you!!! No need to .push() at all, just assign. – Francisco A. Cerda Aug 20 '21 at 20:19

score 78 · Answer 2 · edited Oct 07 '20 at 11:38

78

This error occurs in angular when you didn't intialise the array blank.
For an example:

userlist: any[ ];
this.userlist = [ ];

or

userlist: any = [ ];

edited Oct 07 '20 at 11:38

Thilina Koggalage

1,044
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answered Aug 30 '18 at 07:33

Yogesh Aggarwal

994
7
9

2

If you want a safely typed array then, `public _userList: User[] = []` – Aaron Jordan Oct 25 '18 at 06:40

score 30 · Answer 3 · edited May 23 '17 at 12:10

30

order is an Object, not an Array().

push() is for arrays.

Refer to this post

Try this though(but your subobjects have to be Arrays()):

var order = new Array();

// initialize order; n = index
order[n] = new Array();

// and then you can perform push()
order[n].push(some_value);

Or you can just use order as an array of non-array objects:

var order = new Array();

order.push(a[n]);

edited May 23 '17 at 12:10

Community

1
1

answered Jul 19 '14 at 14:38

Kyle Emmanuel

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1

Even if i define it as an array, it still gives me the same error. – d3nm4k Jul 19 '14 at 14:39
@d3nm4k do you just want to put the value of `a[i]` in either position 0, 1, or 2? If so, you don't use `.push()` for that. The `.push()` method is for adding values to the **end** of an array. – Pointy Jul 19 '14 at 14:41

score 17 · Answer 4 · answered Aug 12 '19 at 04:43

17

In most cases you have to initialize the array,

let list: number[] = [];

answered Aug 12 '19 at 04:43

Akitha_MJ

3,882
25
20

score 4 · Answer 5 · answered Dec 12 '19 at 05:57

4

I fixed in the below way with typescript

Define and initialize firest

pageNumbers: number[] = [];

than populate it

for (let i = 1; i < 201; i++) {
    this.pageNumbers.push(i);
}

answered Dec 12 '19 at 05:57

Shahid Hussain Abbasi

2,508
16
10

score 3 · Answer 6 · answered Feb 12 '21 at 05:53

Generally, Push method is used to add elements at the end of an array.

Here, you have used the push method to an object and not an array which is 'order'.

Steps to debug...

Change the object into an empty array,

var order = [], stack = [];

Now you can use the push method for this array as usual.

To use push method to this 'order' array; you should not use the array index when calling push method to an array. Just use the name of the array only.

var order = [], stack = [];

for(var i = 0; i<a.length; i++){

   if(parseInt(a[i].daysleft) == 0){ 
     order.push(a[i]); 
   }

   if(parseInt(a[i].daysleft) > 0){ 
     order.push(a[i]); 
   }

   if(parseInt(a[i].daysleft) < 0){ 
     order.push(a[i]); 
   }
}

score 2 · Answer 7 · edited Nov 10 '17 at 14:39

2

You do not need to give an index.

Instead of doing order[0].push(a[i]), just do order.push(a[i]).

edited Nov 10 '17 at 14:39

CyanCoding

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answered Nov 10 '17 at 14:02

Manish

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score 1 · Answer 8 · answered Mar 04 '16 at 06:44

answer to your question is simple order is not a object make it an array. var order = new Array(); order.push(/item to push/); when ever this error appears just check the left of which property the error is in this case it is push which is order[] so it is undefined.

score 0 · Answer 9 · answered Aug 10 '16 at 04:14

0

order[] is undefined that's why

Just define order[1]...[n] to = some value

this should fix it

answered Aug 10 '16 at 04:14

Jimma

1

score 0 · Answer 10 · answered Sep 01 '23 at 12:38

0

Make sure add logical AND (&&) before.

let users = [{id: 1, name: 'amoos'}, {id: 2, name: 'rifat'}]
let newUser = {id: 3, name: 'someone'} 
    users && users.push(newUser)    
    console.log('After', users)

answered Sep 01 '23 at 12:38

GMKHussain

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Cannot read property 'push' of undefined when combining arrays

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