生成一个数组,长度为a,内容都是b

         // 递归法
        function createArr(m,n){
            var arr=[];
            function addEle(count,ele){
                if(count!=0){
                    arr.push(ele)
                    count=count-1;
                    addEle(count,ele)
                }
            }
            addEle(m,n)
            return arr
        }
        console.log(createArr(4,'c'))

        // 字符串法
        function createArr1(m,n){
            return Array(m).join(',').split(',').map(()=>n)
        }
        console.log(createArr1(5,'b'))
        // es6法
        let fun = (m,n)=> new Array(m).fill(n);
        console.log(fun(10,'c'))

        let fun1 = (m,n)=> Array.apply(null,new Array(m))
                            .map(()=>n)
        console.log(fun1(6,'d'))

        let fun2 = (m,n)=>Array.from(new Array(m),item=>n)
        console.log(fun2(6,'d'))