Javascript 函数和模块定义

匿名函数

// calculator.js
(function(root) {
  var calculator = {
    sum: function(a, b) { return a + b; }
  };
  root.Calculator = calculator;
})(this);

// app.js
console.log(Calculator.sum(1, 2)); // => 3 

一个例子：

(function (root, ns, factory) {
    // some code
} (window, 'detectZoom', function() {
    // some more code
}));

There is an anonymous function taking three parameters (root, ns, factory) which is immediately invoked.

• root takes the value of`window.
• ns takes the value of 'detectZoom'
• factory takes the value of callback function (also anonymous)

The explanation:

(function (root, ns, factory) {
   // the body of the anonymous function
} (window, 'detectZoom', function() {
   // the body of the 'factory' callback
}));

To break it apart, how to get to this code in four steps:

 1.
 // Anonymous function.
 (function (root, ns, factory) {/* body */});

 2.
 // Anonynmous function, immediately invoked
 (function (root, ns, factory) {/* body */})();  // parentheses mean it's invoked

 3.
 // Callback as a separate argument
 var cbk = function () {};
 (function (root, ns, factory) {/* body */})(window, 'detectZoom', cbk);

 4.
 // Callback as an anonymous function
 (function (root, ns, factory) {/* body */})(window, 'detectZoom', function () {});

You could rewrite your code to be more verbose:

var outer = function (root, ns, factory) {
  // the body
};

var callback = function () {
  // the body
};

outer(window, 'detectZoom', callback);

三种模块定义方式
1） es6

// calculator.js
export function sum(a, b) {
  return a + b;
};

// app.js
import calculator from "calculator";

console.log(calculator.sum(1, 2));

2. common

// calculator.js
module.exports.sum = function (a, b) {
  return a + b;
};

// app.js
var calculator = require("calculator");

console.log(calculator.sum(1, 2));

3. Amd
// calculator.js
define({
  sum: function(a, b) {
    return a + b;
  }
});

// app.js
define(["./calculator"], function(calculator) {
  console.log(calculator.sum(1, 2));
});