JavaScript check if array object exists or undefined

Question

How do I add push a new object into the array if it doesn't exist?

I check this link: How to check if array element exists or not in javascript?

but not sure how to push the new object though!

var element = [];

element['obj'] = 'one';

if (typeof element['obj']['bg'] === 'undefined') {

  console.log('not defined');

  element['obj']['bg'] = 'red';

  console.log(element);

} else {
  console.log('defined');
}

How about `element.push({'bg':'red'});` ? It's a bit unclear what you're asking. Could you be more specific? — Daniel B, Jul 09 '15 at 10:11
What exactly are you trying to achieve? `element['obj'] = 'one';` --> this initialises `element['obj']` to string, and then you want to add a key/value pair to that (string)? — SDekov, Jul 09 '15 at 10:12
You want to use `array` or `object`? `element['obj'] = 'one';` create attr `obj` on `element`, but its not account to length. — fuyushimoya, Jul 09 '15 at 10:14
I don't understand what your code do. But if `element['obj'] = 'one'`, when you do `element['obj']['bg'] === 'undefined'` it's equals to `'one'['bg']`. I think It has no sense. — Sapikelio, Jul 09 '15 at 10:25

score 2 · Answer 1 · answered Jul 09 '15 at 10:12

2

The element is of type string, not an object or an array.

Change the particular variable to an array:

var element = {};
element['obj'] = ['one'];
if ( typeof element['obj']['bg'] === 'undefined' ) {
    console.log('not defined');
    element['obj']['bg'] = 'red';
    console.log(element);
} else {
    console.log('defined');
}

Or better an object:

element['obj'] = {};
element['obj']['id'] = 'one';

The string objects are immutable objects.

answered Jul 09 '15 at 10:12

Praveen Kumar Purushothaman

164,888
24
203
252

But is set `bg` on an `array` is a good practice? Maybe we should wait OP to explain about what structure he expect. – fuyushimoya Jul 09 '15 at 10:17
@fuyushimoya Understand the situation... He's just setting a value. That's all! The OP doesn't mean any CSS or specific stuff here. `:)` – Praveen Kumar Purushothaman Jul 09 '15 at 10:17
1

Yeah.. I agree you, this is the expect of the OP from his code. – fuyushimoya Jul 09 '15 at 10:19

R3tep · Accepted Answer · 2015-09-11T14:15:24.770

var element = []; defines an array and not an object. To push a new value into an array you need to use the push method :

element.push({'obj' : 'one'});

But I think you do not need to create an array here, but just create an object. Declare your object like var element = {};

Like this the line element['obj'] = 'one'; works, you have an object with the key obj and the value one.

When you write element['obj']['bg'] you try to access on an object inside an object. So before set the value red into you need create the object :

element['obj'] = {};
element['obj']['bg'] = 'red';

Full example :

var element = {};

element['obj'] = {};

if (typeof element['obj']['bg'] === 'undefined') {

  console.log('not defined');

  element['obj']['bg'] = 'red';

  console.log(element);

} else {
  console.log('defined');
}

score 1 · Answer 3 · edited Jul 09 '15 at 10:18

1

Try inserting an empty array beforehand;

var element = [];

element['obj'] = 'one';

if ( typeof element['obj']['bg'] === 'undefined' ) {

    console.log('not defined');

    element['obj'] = [element['obj']];

    element['obj']['bg'] = 'red';

    console.log( element);

} else {
    console.log('defined');
}

edited Jul 09 '15 at 10:18

Praveen Kumar Purushothaman

164,888
24
203
252

answered Jul 09 '15 at 10:12

buræquete

14,226
4
44
89

Original value goes off! – Praveen Kumar Purushothaman Jul 09 '15 at 10:13
But you cannot have both element['obj'] = 'one'; and element['obj']['bg'] = 'red'; – buræquete Jul 09 '15 at 10:14
You can have in a way... See my answer. – Praveen Kumar Purushothaman Jul 09 '15 at 10:15
First one means the "obj" indexed value is a string, and the second one requires it to be an array. You have to choose! – buræquete Jul 09 '15 at 10:15
I updated your answer to save the original value. If not, just revert it. Thanks. – Praveen Kumar Purushothaman Jul 09 '15 at 10:18

score 1 · Answer 4 · edited Jul 09 '15 at 10:20

1

var element = [];

element['obj'] = 'one';

if ( typeof element['obj']['bg'] === 'undefined' ) {

    console.log('not defined');

    element['obj'] = {'bg':'red'};

    console.log("My value:"+element['obj']['bg'] );

} else {
    console.log('defined');
}

http://jsfiddle.net/o66uhd05/3/

edited Jul 09 '15 at 10:20

Praveen Kumar Purushothaman

164,888
24
203
252

answered Jul 09 '15 at 10:19

NiRUS

3,901
2
24
50

score 0 · Answer 5 · answered Jul 09 '15 at 10:39

You could try this way.

var element = [],item = [];

item['obj'] = 'one';
element.push(item);

if ( typeof element['obj']['bg'] === 'undefined' ) {

    console.log('not defined');

    item['bg']='red';

    element.push(item);

    console.log( element);

} else {
    console.log('defined');
}

JavaScript check if array object exists or undefined

5 Answers5