The effect of parenthesis with `this` binding in javascript

Question

I encounter a very tricky case:

class C {
  // class method are implicit in strict mode by default
  static method() { return this === undefined; }  
}

C.me         


        

Answer 1

When you use the comma operator in JavaScript, both operands are evaluated, and then the right-most value is returned. The evaluated function value that comes out of the parentheses has no context of where it came from. This can be likened to assigning a value to a variable, where the right-hand side of the assignment operator = is evaluated before the value is assigned:

(0, C.method)();
//  ^^^^^^^^ evaluates here

var func = C.method;
//         ^^^^^^^^ evaluates here
func();

Once a function is put into a variable, it loses all context of what object it came from (unless bind is used). This context is important to determining the value of this. When a function is called without being the member of an object, it defaults to the global object, or undefined if the function is in strict mode. (MDN)