js函数与对象的比较

Question

In this JavaScript code , why the two functions when compared directly returns True while when compared using new object creation returns False?

 function A() { return this; } function B() { return this; } console.log(A() === B()); console.log(new A() == new B()); 

Answer 1

You should be aware that in JavaScript, this refers to the calling context or the place where the call to the function was made.

When you do

function A() {
    return this;
}

then

console.log( A() );

The calling context, for obvious reasons, is the window context and hence, this refers to window . Same is the case with B() .

However, when you do new A() , you initialize a new instance of the class and, vis-a-vis, a new memory location. Since each new initialization refers to a new memory location, they never equate to true .

Answer 2

In first case this inside the function refers to the window object. So it is basically window === window which is true

function A() {
 return this;  // this is the window object
}

function B() {
  return this; // this is window object
}

In this case new A() and new B() refers to the different memory location, so they are never equal