调用不带括号的函数将整个函数作为字符串返回 [英] Calling a function without parentheses returns whole function as a string

问题描述

我创建了一个JavaScript对象，如下所示:

I created a JavaScript object like this:

var obj = {
  a: 10,
  b: 20,
  add: function(){
     return this.a + this.b;
  }
};

我以 obj.add 的形式执行该函数，它以字符串形式返回整个函数，如下所示:

I executed the function as obj.add and it returns the whole function as string a like this:

function(){
  return this.a + this.b;
}

But later, I tried to call the function again, including the parentheses, like `obj.add()` and it returns the value `30`. I couldn’t figure out why I get such a different output upon calling the function with `obj.add` and with `obj.add()`. What is the main difference between calling an object’s function with parentheses and without parentheses?

推荐答案

在没有括号的情况下，您正在检索对该函数的引用，而不是在调用(执行)该函数

Without parentheses, you're retrieving a reference to the function, you are not calling (executing) the function

在括号中，您正在执行该函数.

With parentheses, you're executing the function.

function a() {
  return 2;
}

var b = a(); // called a, b is now 2;
var c = a; // c is referencing the same function as a
console.log(c); // console will display the text of the function in some browsers
var d = c(); // But it is indeed a function, you can call c(), d is now 2;

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