js函数基础练习

考察变量提升、函数提升、作用域。

            var a = 10
            function fun1(){
                console.log(a) //undefined
                var a = 11
            }
            fun1()
            console.log(a)//10
            
            var b = 20
            function fun2(){
                console.log(b) //20
                b = 21
            }
            fun2()
            console.log(b)//21
            
            var c = 30
            function fun3(c){
                console.log(c) //undefined
                c = 31
            }
            fun3()
            console.log(c)//30

            var d = 40
            function fun4(d){
                console.log(d) //555
                d = 31
            }
            fun4(555)
            console.log(d)//40