Typescript cannot set property of undefined

Question

Can someone please explain why you can't do this in Typescript?

this.obj.id = 1;
this.obj.str = 'This is string';

But you can do this:

this.obj = { id: 1, str: 'This is string'};

What is this.obj initially? If you didn't define it, you're trying to define properties on something that doesn't exist. — jhpratt
– jhpratt, Commented Jan 25, 2019 at 3:11

Mukyuu · Accepted Answer · 2019-01-25 03:18:15Z

3

It's not a matter of you can't do but, you're doing it wrong. See Stackblitz Demo

I was able to define by using it like this:

obj = [];
obj2 = { id: 0, str: '' };
  
this.obj = { id: 1, str: 'This is string' };
this.obj2.id = 1;
this.obj2.str = 'This is string';
console.log(this.obj)
console.log(this.obj2)

answered Jan 25, 2019 at 3:18

Mukyuu

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1 Comment

Chinito Over a year ago

Thank you. I already know why. You cannot set property of undefined. So you should initialize a default value or empty value.

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