数组、字符串方法混合训练

1. 将let’s go home变为s’tel og emoh

        var str = "let's go home";
        /* s'tel og emoh */       
        /* 
        1.将字符串分割为数组split(" ")
        ["let's","go","home"] 
        */
        /* [[l,e,t,',s],[g,o],[h,o,m,e]] */
        /* reverse */
        /* [[s,',t,e,l],[o,g],[e,m,o,h]] */
        /* join */
        /* ["s'tel","og","emoh"] */
        /* join */
        /* s'tel og emoh */

map遍历

        var arr = str.split(" ");
        var newArr = arr.map(item=>{
            return item.split("").reverse().join("")
        })
        console.log(newArr.join(" "))

forEach遍历

        var arr = str.split(" ");
        var all = []
        arr.forEach(item=>{
            let i = item.split("").reverse().join("")
            all.push(i)
        })
        console.log(all.join(" "))

2. 筛选tian字音或者“天”开头的城市

        var cities = [{spell:"tianmen",city:"天门"},{spell:"tianshui",city:"天水"},
        {spell:"tianjin",city:"天津"},{spell:"wuhan",city:"武汉"},
        {spell:"tianzifang",city:"田子坊"}]
        var arr = []
        cities.forEach((item,index)=>{
            if(item.spell.startsWith("tian")||item.city.startsWith("天")){
                arr.push(item.city)
            }
        }        
        )
        console.log(arr)
          //"天门""天水" "天津" "田子坊"

3. map()+join()

        <script>
        var obj = [{name:"汪峰",age:10},{name:"赵雷",age:5},{name:"房东的猫",age:6}]
        /* 1.["汪峰","赵雷","房东的猫"] */
        /* 2. 汪峰/赵雷/房东的猫*/
        /* allName = "汪峰/赵雷/房东的猫" */
        var newArr = obj.map(item=>{
            return item.name
        })
        console.log(newArr.join("/"))
    </script>

4. sum

    <script>
        var arr = [{price:4,count:2},{price:5,count:3},{price:6,count:3}];
        function sum(arr){
            var total = 0;
            /* 8  23 41*/
            arr.forEach(item=>{
                total=item['price']*item['count']+total
            })
            return total;
        }
        console.log(sum(arr))
    </script>