通过示例彻底搞懂js闭包

function sayHello(name) 
{
 var text = 'Hello ' + name;
 var sayAlert = function() { console.log(text); }
 sayAlert();
}

sayHello("Bob") // 输出"Hello Bob"

function sayHello2(name) 
{
 var text = 'Hello ' + name; // 局部变量
 var sayAlert = function() { console.log(text); }
 return sayAlert;
}

var say2 = sayHello2("Jane");
say2(); // 输出"Hello Jane"

function buildList(list) {
 var result = [];
 for(var i = 0; i < list.length; i++) {
  var item = 'item' + list[i];
  result.push( 
    function() {
      console.log(item + ' ' + list[i]);
    } 
   );
 }
 return result;
}

var fnlist = buildList([1,2,3]);
for (var j = 0; j < fnlist.length; j++) {
  fnlist[j](); 
}

function buildList(list) {
 var result = [];
 for(var i = 0; i < list.length; i++) {
  var item = 'item' + list[i];
  result.push( 
    (function(i) {
      console.log(item + ' ' + list[i]);
    })(i)
   );
 }
 return result;
}

var fnlist = buildList([1,2,3]);

item1 1
item2 2
item3 3

function newClosure(someNum, someRef) 
{
 var anArray = [1,2,3];
 var num = someNum;
 var ref = someRef;
 return function(x) 
 {
 num += x;
 anArray.push(num);
 console.log('num: ' + num + "; " + 'anArray ' + anArray.toString() + "; " + 'ref.someVar ' + ref.someVar);
 }
}
closure1 = newClosure(40, {someVar: "closure 1"}); 
closure2 = newClosure(1000, {someVar: "closure 2"}); 
closure1(5); // 打印"num: 45; anArray 1,2,3,45; ref.someVar closure 1"
closure2(-10); // 打印"num: 990; anArray 1,2,3,990; ref.someVar closure 2"

function sayAlice() 
{
 var sayAlert = function() { console.log(alice); }
 var alice = 'Hello Alice';
 return sayAlert;
}

var sayAlice2 = sayAlice();
sayAlice2(); // 输出"Hello Alice"

function setupSomeGlobals() {
 var num = 666;
 gAlertNumber = function() { console.log(num); }
 gIncreaseNumber = function() { num++; }
 gSetNumber = function(x) { num = x; }
}
setupSomeGlobals();
gAlertNumber(); // 输出666
gIncreaseNumber();
gAlertNumber(); // 输出667
gSetNumber(5);
gAlertNumber(); // 输出5