JS面试1

window.number = 1
var obj = {
    'number':4,
    'dbl':(function(){
        this.number *=2
        return function(){
            this.number *=2
        }
    })()
}
var dbl = obj.dbl
dbl()
obj.dbl()
console.log(window.number + obj.number)

执行函数dbl 时，this指向了window， 所以window.number = 122 = 4,执行 函数obj.dbl()时，this指向了obj，所以 obj.number = 8, 最终结果为12

function C1(name){if(name) this.name = name}
function C2(name){this.name=name}
function C3(name){this.name = name || 'John';}

C1.prototype.name = 'Tom';
C2.prototype.name = 'Tom';
C3.prototype.name = 'Tom';
console.log((new C1()).name + (new C2()).name + (new C3()).name)

(new C1()).name 没有传值，在C1.prototype上取值，所以是’Tom’
(new C1()).name 没有传值，默认是undifined，所以name 值 为 undifined
(new C1()).name 没有传值，默认是 ‘John’，所以name 值 为 ‘John’

//请定义这样一个函数
function repeat (func, times, wait) {

}
//这个函数能返回一个新函数，比如这样用
var repeatedFun = repeat(console.log, 3, 2000)
//调用这个 repeatedFun ("hellworld")
//会alert十次 helloworld, 每次间隔5秒
function repeat (func, times, wait) {
    return function(){
        var handle,i=0,arg=arguments
        handle = setInterval(function(){
            if(++i === times){
                clearInterval(handle)
            }
            return func.apply(null,arg)
        },wait)
    }
}
var repeatedFun = repeat(console.log, 3, 2000)
repeatedFun ("hellworld")