function init() {
 var name = 'Mozilla'; // name is a local variable created by init
 function displayName() { // displayName() is the inner function, a closure
 alert(name); // use variable declared in the parent function 
 }
 displayName(); 
}
init();

because inner functions have access to the variables of outer functions, displayName() can access the variable name declared in the parent function, init().

var data = [
 {'key':0},
 {'key':1},
 {'key':2}
];
function showKey() {
 for(var i=0;i<data.length;i++) {
 setTimeout(function(){
 //console.log(i); //發現i

var data = [
 {'key':0},
 {'key':1},
 {'key':2}
];
function showKey() {
 var f1 = function(n){
 data[i].key = data[i].key + 10;
 console.log(data[i].key)
 }
 for(var i=0;i<data.length;i++) {
 setTimeout(f1(i), 1000);
 }
}
showKey();
// 得到預期的 10 11 12