Typescript cannot set a property of undefined

Question

I have the following in my Angular component:

class Test implements ....{
  duration:{from:number, to:number}

  constructor(){
    this.duration.from = "ddd";//set after some calculations
     this.duration.to = "ddd";
  }
}

The above returns an error of "cannot set property from of undefined".

Where am I going wrong?

You did declare that duration was of type {from:number, to:number}. That does not initialize it. this.duration is undefined at the time the constructor runs. Use this.duration = {from: 'ddd', to: 'ddd'} to initialize it. — Raphael Schweikert
– Raphael Schweikert, Commented Feb 18, 2018 at 20:26

krivtom · Accepted Answer · 2018-02-18 20:30:47Z

5

In your class you define variable duration and specify it's type, however you do not initialize it, so the value of the variable remains undefined. Instead of assigning properties this.duration.from and this.duration.to, you should initialize variable:

class Test implements ....{
    duration:{from:number, to:number}

    constructor(){
        this.duration = {
            from: 1,
            to: 2
        };
    }
}

answered Feb 18, 2018 at 20:30

krivtom

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