TypeScript中的对象定义

Question

I currently have the following, in a TypeScript app:

interface Data {
    url: string,
    // more stuff
}

(...)

export class something() {
    public data: Data;
}

method(){
    this.data.url = "things";
}

The issue is that every time i try to give data.url a value, I get an error saying I cannot set the property url of undefined. What am I doing wrong? And why?

Thanks in advance!

Answer 1

1) The class declaration syntax is wrong, it should be

export class something { 
}

and NOT

export class something() { 
}

2) method is defined outside of the class, it should be inside the class

3) this.data is not instantiated, it's undefined , and you're trying to access url property of an undefined variable, hence the error.

interface Data {
    url: string,
    // more stuff
}

(...)

export class something {
    public data: Data;
    method(){
        this.data = {
           url: "things",
           // more stuff
        }
    }
}

If you want to access method from outside of the class, then you need to instantiate the class something .

method() {
    let obj = new something();
    obj.data = {
        url: "things",
        // more stuff
    }
}