TSLint double vs triple equality

Question

I know that a single equality sign means assignment; double means equality; and triple means equality and the same type.

What I don't understand why the typescript linter would want me to use triple equality signs in this case:

function gcf(a: number, b: number): number {     return (b == 0) ? (a) : (gcf(b, a % b)); } 

TsLint: == should be ===

I know that 0 is a number and I also know that b is a number (or else I'll get a compilation error). So why would I want to use triple equality signs in this case?

Answer 1

Types can't save you from all errors caused by ==. Particularly since undefined and null are compatible with all types. e.g. the following is an incorrect if :

var foo:number = null;   if (foo == undefined) {      console.log('is undefined'); // actually null   } 

For more info on why these are equal https://stackoverflow.com/a/359509/95190

Personally : I have had this rule disabled and never had any issues. I don't compare with true/false/null/undefined, just if them. And typescript prevents comparing strings and numbers so that is not an error I need to deal with.