javascript

Hoisting

var v='Hello World';
(function(){
    alert(v);
    var v='I love you';
})()

var v='Hello World';
(function(){
    var v;
    alert(v);
    v='I love you';
})()

//结果是undefined

//scope
 var x = 1;
    console.log(x); // 1
 if (true) {
   var x = 2;
   console.log(x); //2
}
 console.log(x);// 2
 
//建立临时scope
function foo() {
    var x = 1;
    if (x) {
        (function () {
            var x = 2;
            // some other code
        }());
    }
    // x is still 1.
}

浏览器编译js差异

// 不同浏览器编译差异

if ( condition ) {
  function A () {
  }
}

console.log(A)

//在火狐下不会预编译

自定义log

//log ＝ console.log 无效

log = console.log.bind(console)

闭包

  function say667() {
    // Local variable that ends up within closure
    var num = 666;
    var sayAlert = function() { alert(num); }
    num++;
    return sayAlert;
}

 var sayAlert = say667();
 sayAlert()//执行结果应该弹出的667