Problem with constructor containing an interface

Question

So I have this typescript class with an interface implemented in the constructor parameter:

    interface responseObject {
      a: string;
      b: boolean;
      c?: boolean; 
   }

   class x
   {
     a: string;
     b: boolean;
     c: boolean; 
     constructor(args: responseObject) {
       //check if non optional parameters are not supplied
       if(!args.a || !args.b) throw new Error("Error"); 
       //Trying to initialize class data member -> not working
       this.a = args.a;
       this.b = args.b;
     }
   }

Now I have two questions, my first one is how can I access the different parameters supplied inside args, for example how could I check if they are both supplied (something that looks like the thing I tried !args.a or !args.b) and my second question is how can I supply a default value for c if it is not supplied?

Thanks in advance.

Alex · Accepted Answer · 2020-03-20 19:47:49Z

1

You could do that.

constructor({ a, b, c = 'defaultValue' }) {
    //check if non optional parameters are not supplied
    if(!a || !b) throw new Error("Error"); 
}

Note that you have to explicitly throw the error, there is no short syntax for that.

edited Mar 20, 2020 at 19:47

Alex

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answered Mar 20, 2020 at 19:43

Guerric P

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6 Comments

Alex Over a year ago

Thank you for your response, however would that be possible using an interface and also declaring c as optional?

Guerric P Over a year ago

An interface has no JavaScript representation so it's unable to do runtime checking

Alex Over a year ago

Oh ok @Guerric P , and if I want c to be optional should I include ? or not because there is already a default value?

Alex Over a year ago

ok, thank you! also last question, if I let's say want to access interface properties how would I do that, like is there something I could use like args.a?

Guerric P Over a year ago

You can use arguments: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

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