Add type predicate to Boolean (BooleanConstructor) #32834

Suggestion

Add an overload to Boolean defintion

 interface BooleanConstructor {
     new(value?: any): Boolean;
-    <T>(value?: T): boolean;
+    <T>(value?: T): value is Exclude<T, false | null | undefined | 0 | ''>
     readonly prototype: Boolean;
 }

playground

Use Cases

Array.filter

declare const actions: Array<(() => void) | null | undefined>
actions.filter(Boolean).forEach(act => act())

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.