方法和函数有什么区别？ 如何声明方法？

Question

I am learning Javascript on Codecademy. As my understanding Method is a function associated with the objects. I think to call it a method it should inside an object. Is it? Should I really fully understand main difference between functions and methods to write error free code. This is very confusing to me.

Below it the Codecademy code, they say on line 2 'setAge' is a Method where it is clearly looks like a function. It is not even related to any Object yet. Coz it is not even inside of any object.

// here we define our method using "this", before we even introduce bob
var setAge = function (newAge) {
  this.age = newAge;
};

// now we make bob
var bob = new Object();
bob.age = 30;
bob.setAge = setAge;

// make susan here, and first give her an age of 25
var susan = new Object();
susan.age = 25;
susan.setAge = setAge;
susan.setAge(35);
// here, update Susan's age to 35 using the method

Answer 1

That's a good question, I could see how that could be confusing. It appears that they are referring to it as a method because they later modify the bob object to include the function, thereby making it a "method".

var setAge = function (newAge) {
  // using "this" sometimes indicates
  // that a function may instead be an object method
  this.age = newAge;
};

// becomes a method
bob.setAge = setAge;

Their code is equivalent to the following:

bob.setAge = function (newAge) {
  this.age = newAge;
};

You are right in your understanding about methods.

Answer 2

As others have said, a method and a function have a lot in common, in fact all methods are functions.

The biggest difference is that a method is attached to an object and the this value gets set when that object is called.

I've made a snippet to demonstrate

 "use strict"; var bob = { bool: true }; bob.test = function() { console.log("this = ", this); }; console.log("Here is bob test and 'this'"); bob.test(); // Separate the method var tmp = bob.test; // In strict mode, this will be undefined. // In non-strict, it will be the same as `window` tmp();