Typescript property does not exist on type {}

Question

I have the following code in Typescript. Why does the compiler throws an error?

var object = {};
Object.defineProperty(object, \'first\', {
         


        

Answer 1

Make the object type any:

var object: any = {};

Answer 2

Another way is to do interface, so compiler will know that property exists.

interface IFirst{
  first:number;
}


let object = {} as IFirst;
Object.defineProperty(object, 'first', {
  value: 37,
  writable: false,
  enumerable: true,
  configurable: true
});
console.log('first property: ' + object.first);

Take a look at this question How to customize properties in TypeScript

Answer 3

In the given case, I would just rewrite it as

var object = {};

var withFirst =  {...object, get first() {return 37;}};

console.log('first property: ' + withFirst.first);

Answer 4

That's because Typescript is a strict type language. When you create a variable and give to it a type, you can't access properties that does not exists in that type. After adding extra property will not force the compiler to look for it. If you need to add a property after the creation, make the type of your variable any.