Why does typescript not complain about certain undefined variables

Question

I have the following example:

class Uncle {
  constructor(public name : string) { }

  talk() {
    return "Hello my name is " + name;
  }
}

let p : Uncle = new Uncle("Jo");
console.log(p.talk());

For certain variable names, typescript (right now Version 2.1.4 ) will not complain that they are not defined in your program (In the method talk, name is being used without this.). name is one of those.

If I rename the variable to, say, firstName , the compiler complains rightfully...

error TS2663: Cannot find name 'firstName'. Did you mean the instance member 'this.firstName'?

Same goes for eg window, which is apparently assumed to exist.

My question(s) are:

• Which variable names are assumed to exist and why?
• Can that behaviour be changed (eg in some linters you can state which variables you expect to be globally available)?

Answer 1

The reason it won't complain about name is that there's a variable called name in the global namespace.
Open the console in the developer tools and write name and press enter and you'll receive: "" .

More resources:

• Mdn page on the property
• Definition in the lib.es6.d.ts

All global variables can be used without defining them.

In order to remove all global definitions you can, eg in your tsconfig.json , set the "libs" option to an empty array. This will remove all globals.