自执行匿名函数语法和普通函数语法对比

var eatFunction = function (what_to_eat) {
  var sentence = 'I am going to eat a ' + what_to_eat;
  console.log( sentence );
};
eatFunction( 'sandwich' );

// is the same as

(function (what_to_eat) {
  var sentence = 'I am going to eat a ' + what_to_eat;
  console.log(sentence);
})('sandwich');

// is the same as

(function (what_to_eat) {
  var sentence = 'I am going to eat a ' + what_to_eat;
  console.log(sentence);
}('sandwich')); 

// Three of them output 'I am going to eat a sandwich'

  唯一的区别是，变量 eatFunction 被移除了，使用一对括号把函数定义包了起来。

示例：

自执行匿名函数

var counter = (function() {
  var count = 0;
  var get = function() {
    count++;
    return count;
  }
  return get;
})();

console.log(counter()); //输出 1
console.log(counter()); //输出 3
console.log(counter()); //输出 3

 普通函数

var generateClosure = function() {
  var count = 0;
  var get = function() {
    count++;
    return count;
  }
  return get;
};

var counter = generateClosure();
console.log(counter()); //输出 1
console.log(counter()); //输出 3
console.log(counter()); //输出 3