3. 作用域 %26 变量提升 %26 闭包

1、 阅读代码

(function(){
   var x = y = 1;
})();
var z;
console.log(y); 
console.log(z); 
console.log(x);

2、 阅读代码

var a, b
(function () {
   console.log(a);
   console.log(b);
   var a = (b = 3);
   console.log(a);
   console.log(b);   
})()
console.log(a);
console.log(b);

3、 阅读代码

var friendName = 'World';
(function() {
  if (typeof friendName === 'undefined') {
    var friendName = 'Jack';
    console.log('Goodbye ' + friendName);
  } else {
    console.log('Hello ' + friendName);
  }
})();

4、 阅读代码

function fn1(){
  console.log('fn1')
}
var fn2
fn1()
fn2()
fn2 = function() {
  console.log('fn2')
}
fn2()

5、 阅读代码

function a() {
    var temp = 10;
    function b() {
        console.log(temp); // 10
    }
    b();
}
a();
function a() {
    var temp = 10;
    b();
}
function b() {
    console.log(temp); // 报错 Uncaught ReferenceError: temp is not defined
}
a();

6、 阅读代码

 var a=3;
 function c(){
    alert(a);
 }
 (function(){
  var a=4;
  c();
 })();

7、 阅读代码

function fun(n, o) {
  console.log(o)
  return {
    fun: function(m){
      return fun(m, n);
    }
  };
}
var a = fun(0);  a.fun(1);  a.fun(2);  a.fun(3);
var b = fun(0).fun(1).fun(2).fun(3);
var c = fun(0).fun(1);  c.fun(2);  c.fun(3);

8、 阅读代码

f = function() {return true;};   
g = function() {return false;};   
(function() {   
   if (g() && [] == ![]) {   
      f = function f() {return false;};   
      function g() {return true;}   
   }   
})();   
console.log(f());