Typescript conversion to boolean

Question

In Typescript I can do this:

var xxx : some_type;

if (xxx)
    foo();
else
    bar();

Here xxx will be treated as a boolean, regardless of its

Answer 1

foo(!!xxx); // This is the common way of coercing variable to booleans.
// Or less pretty
foo(xxx && true); // Same as foo(xxx || false)

However, you will probably end up duplicating the double bang everytime you invoke foo in your code, so a better solution is to move the coerce to boolean inside the function DRY

foo(xxx);

foo(b: any){
  const _b = !!b;
  // Do foo with _b ...
}
  /*** OR ***/
foo(b: any){
  if(b){
    // Do foo ...
  }
}

Answer 2

While you can't cast a number directly to a boolean, you can cast it to the wrapper Boolean class and immediately unwrap it. For example:

foo(<boolean><Boolean>xxx);

While clumsy, it avoids the type erasure of casting to <any>. It's also arguably less obscure & more readable than the !! approach (certainly so in the transpiled js code).