Destructuring a function from object ( Date Object )

Answer 1

Because this it not a Date object. When you call getDate() without its proper context (ie. date.getDate()), then you're calling it in the context of the window (or null in strict mode). Neither window nor null are Date objects, therefore the function fails.

Try const getDate = date.getDate.bind(date);

Demo:

const test = { fn : function() { return this.constructor; } };

const normal = test.fn();
console.log(normal); // object

const {fn} = test;
console.log( fn() ); // window

const bound = test.fn.bind(test);
console.log( bound() ); // object