Javascript class constructor with parameter used as key from object literal

Question

Title might be a little confusing, but I have following problem:

var propertyList = {
    type1: {property1: 1},
    type2: {property1: 2}
}

class Test {
    constructor(typ){
        this.property1 = propertyList.typ.property1;
    }
}

var a = new Test('type1');

Code is pretty self-explanatory - I want to set property1 property of a object not by passing value manually in constructor, but rather chosing one of values from propertyList object literal by passing one of its key to constructor. I expected that when I run above code, object a will be created with property1 value set to 1. However instead of that I got Uncaught TypeError: Cannot read property 'property1' of undefined error. When I pust console.log(typ) in the first line of constructor, it correctly shows that value passed into constructor is type1. Why above code doesn't work and can it be fixed somehow?

You need to use this syntax : `propertyList[typ].property1` otherwise it will look for the property name **typ** in the propertyList object (and this property doesn't exist) — Olivier Boissé, Aug 05 '16 at 12:28

score 0 · Accepted Answer · answered Aug 05 '16 at 12:40

Your syntax is a little off. You can't use the passed-in argument typ in your assignment like that because the code will then actually look for the property typ within propertyList (like propertyList { typ: }). To use your passed-in argument, wrap it in brackets:

this.property1 = propertyList[typ].property1;

Javascript class constructor with parameter used as key from object literal

1 Answers1