无论外部变量如何变化，如何在函数中引用自身？

Question

I have a function which has other functions defined:

var A = function(n) {
  console.log(n + A.num());
}
A.num = function() {
  return 5;
}

I want to change the name to B and delete A :

var B = A;
A = undefined;

But, when I do B() , It gives an error throws: "Cannot read property 'num' of undefined", which is completely normal and expected.

How do I handle this?

PS : Anyone who thinks that changing A.num() with this.num() , It will not work

Answer 1

You can always refer to the current function using its explicit name (if it has one).

So, change the definition, to name the function, and refer to it using that:

 var A = function currentFunction(n) { console.log(n + currentFunction.num()); } A.num = function() { return 5; } var B = A; A = undefined; B(10); //15 console.log(typeof currentFunction) //undefined, function name is local

Note: the abovementioned approach won't work if the function is named implicitly, but will continue to work if the function is renamed via fn.name

---

Alternatively, if the function isn't an arrow function, you can also use arguments.callee , that will work even with anonymous functions, but its use isn't recommended:

 var A = function (n) { console.log(n + arguments.callee.num()); } A.num = function() { return 5; } var B = A; A = undefined; B(10); //15

Unfortunately, none of the above will work with arrow functions, if you want to refer to itself, use a named bound function expression instead.

Answer 2

actually that's normal, because in js you can't really copy object

// Define object bar
var bar = {
   x : 'Hi'
}
console.log(bar.x);  //Hi

// Assign it to foo
var foo = bar;
console.log(foo.x);  //Hi

//But
foo.x = 'Hello!! Im foo.';
console.log(foo.x);  //Hello!! Im foo.
console.log(bar.x);  //Hello!! Im foo.

bar.x = "Nice to meet you foo!!";
console.log(foo.x);  //Nice to meet you foo!!
console.log(bar.x);  //Nice to meet you foo!!

you have to return a new one with the same value as the last

var foo = {...bar};

and this is not working because B is always calling 'num' from A that doesn't exist, One way to sever the parity would be stringify the initial function, then use a function constructor to create the clone after replacing the 'A' by 'B' but tell me more why are you facing this problem ?

Answer 3

 var A = function(n) { if(!this.num){ console.log("This is not available coz obj is not created"); console.log("Below error is for testing purpose"); } let a=this.num(n); console.log(a); } //use prototype here //A.num = function() { A.prototype.num=function(n){ return n+5; } //use new to create object new A(5); var B = A; A = undefined; //use new to create object new B(6); B(5);//lets try without using new keyword

 .as-console-wrapper { max-height: 100% !important; top: 0; }