React Native/Javascript - How to know that object does not have the property?

Question

Let say :

myVariable.color;
myVariable.height;
myVariable.width;

But sometimes, myVariable only have "color" and "height" property.

I have try this, but no luck :

if(myVariable.width == undefined) {
//but not filtered here
}

How to know if myVariable doesn't contain "width" property by code, is it possible ?

score 0 · Answer 1 · answered Jul 01 '19 at 07:34

0

You could try to double negate:

if(!!myVariable.width){
    //do something here
}

answered Jul 01 '19 at 07:34

Mihai Iorga

Nope, not the answer. – Isaaс Weisberg Jul 01 '19 at 07:34
@IsaacCarolWeisberg I know about `hasOwnProperty` but .. what's wrong with above code? Why isn't it the answer .. It does not do what it should do? – Mihai Iorga Jul 01 '19 at 07:38
The thing is that you could've assigned `undefined` to the `width` yourself, or alternatively you could have never assigned to `width` anything in the first place. But: if you have never touched the property setter, then `hasOwnProperty` and `in` will return false. However, if you assign `undefined` to `width` manually, your check will still fail since the value is `undefined`, but `hasOwnProperty` and `in` will be both true because this key was actually set. – Isaaс Weisberg Jul 01 '19 at 08:19

Isaaс Weisberg · Answer 2 · 2019-07-01T07:36:56.647

0

You are looking for hasOwnProperty.

If you would like to perform a search in the whole potential prototype chain of an object, you can also use the in operator.

if (width in object) {

edited Jul 01 '19 at 07:36

answered Jul 01 '19 at 07:34

Isaaс Weisberg

Is it secure if implement in React Native ? – Crocodile Jul 01 '19 at 07:34
Yes, this is a feature of JS runtime and not the browser/node specifically. – Isaaс Weisberg Jul 01 '19 at 07:35

2 Answers2