JS进阶-闭包的几种常见形式

//作用域链 ???var a = 1; ???function test() { ???????var b =2; ???????return a; ???} ???alert(test());//弹出1； ???alert(b);//不能获取b

//scope chain ???var a = 1; ???function test() { ???????var b = 2; ???????function test1() { ???????????var c = 3; ???????????alert(a); ???????????alert(b); ???????????alert(c); ???????} ???????test1(); ???} ???test();//弹出1，弹出2，弹出3；

//词法作用域； ???function f1() { ???????var a = 12; ???????return f2(); ???} ???function f2() { ???????return a; ???} ???alert(f1());//并不能获取a，a在f2()中并未定义；

function f1() { ???????var a = 1; ???????return f2(); ???} ???function f2() { ???????var b = 3; ???????alert(b); ???????return a; ???} ???alert(f1());//弹出3，a在f2()中未定义

function f1() { ???????var a = 1; ???????return f2(); ???} ???function f2() { ???????var b = 3; ???????alert(b); ???????return a; ???} ???alert(f1());//弹出3，a在f2()中未定义,undefined ???var a=55; ???alert(f1());//弹出3，弹出55

//通过闭包突破全局作用域链 ???function f() { ???????var a = "sun"; ???????return function () { ???????????return a; ???????} ???} ???var test = f(); ???alert(test());//弹出sun

var n;function f() { ???var a = "sun"; ???n = function () { ???????return a; ???}}f();alert(n());//弹出sun

 ??function f(param) { ???????var n =function () { ???????????return param; ???????}; ???????param++; ???????return n; ???} ???var test = f(45); ???alert(test());//弹出46；