TypeScript hasOwnProperty equivalent

Question

In JavaScript, if I want to loop through a dictionary and set properties of another dictionary, I'd use something like this:

for (let key in dict) {
  if (obj.hasOwnProperty(key)) {
    obj[key] = dict[key];
  }
}

If obj is a TypeScript object (instance of a class), is there a way to perform the same operation?

Solution

If obj is a TypeScript object (instance of a class), is there a way to perform the same operation?

Your JavaScript is valid TypeScript (more). So you can use the same code as it is.

Here is an example:

class Foo{
    foo = 123
}

const dict = new Foo();
const obj = {} as Foo;

for (let key in dict) {
  if (obj.hasOwnProperty(key)) {
    obj[key] = dict[key];
  }
}

Note: I would recommend Object.keys(obj).forEach(k=> even for JavaScript, but that is not the question you are asking here.

Comments

[dSebastien]

I have a side question about this; in your case you initialize the foo property, which ensures that it is present in the generated js code; although if the property is not defined, then it's not part of the generated code at all. Do you know why that is? This surprised me a bit when I tried using hasOwnProperty on some instance and got false back although I expected it to be present but undefined.

[loretoparisi]

Let's consider that undefined properties i.e. all properties that are defined in the typescript class A { prop1:string, prop2:number} will not be enumerated by any of Object.keys or this.hasOwnProperty(k) since the autogen javascript has no knowledge of those properties.

[Coo]

Why would you recommend Object.keys(obj).forEach(k=> over for() ?

[Pang]

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