var i,n,sum//globals
function averageScore(players){
 sum =0;
 for(i = 1, i = player.length; i<n; i++){
  sum += score(players[i]);
 }
 return sum/n;
}

function averageScore(players){
var i,n,sum;
 sum =0;
 for(i = 1, i = player.length; i<n; i++){
  sum += score(players[i]);
 }
 return sum/n;
}

this.foo; //undefined
foo ="global foo"; //"global foo"
this.foo; //"global foo"

var foo ="global foo";
this.foo; //"global foo"
this.foo ="changed";
foo; //"changed"

if(!this.JSON){
 this.JSON ={
  parse:...,
  stringify:...
 }
}

MYAPP.stooge = {
 "first-name": "Joe",
 "last-name": "Howard"
};

MYAPP.flight = {
 airline: "Oceanic",
 number: 815,
 departure: {
  IATA: "SYD",
  time: "2004-09-22 14:55",
  city: "Sydney"
 },
 arrival: {
  IATA: "LAX",
  time: "2004-09-23 10:42",
  city: "Los Angeles"
 }
};

var serial_maker = function ( ) {

// Produce an object that produces unique strings. A
// unique string is made up of two parts: a prefix
// and a sequence number. The object comes with
// methods for setting the prefix and sequence
// number, and a gensym method that produces unique
// strings.

 var prefix = '';
 var seq = 0;
 return {
  set_prefix: function (p) {
   prefix = String(p);
  },
  set_seq: function (s) {
   seq = s;
  },
  gensym: function ( ) {
   var result = prefix + seq;
   seq += 1;
   return result;
  }
 };
}( );

var seqer = serial_maker( );
seqer.set_prefix = 'Q';
seqer.set_seq = 1000;
var unique = seqer.gensym( ); // unique is "Q1000"

( function ( win ) {

 'use strict' ;
 var doc = win.document ;
 //在此定义其他的变量并书写代码
} )

function sum(x, y) {
 // 不推荐写法: 隐式全局变量
 result = x + y;
 return result;
}

function sum(x, y) {
 var result = x + y;
 return result;
}

// 反例，勿使用
function foo() {
 var a = b = 0;
 // ...
}

function foo() {
 var a, b;
 // ... a = b = 0; // 两个均局部变量
}