6-3 字符串常用的方法

1.length属性 //获取字符串的长度

var a = "hello world";
alert(a.length) //11

2.增加

1.concat()

concat() 连接字符串
        var str="hello world"
        /* 增加 */
        str=str.concat("good");  
        console.log(str)  //hello worldgood

3.查询

1.indexof()

        /* indexOf -->可以查询字符串值的下标*/
        console.log(str.indexOf("g"))  //11

2.slice()

3.substring()

4.substr()

    <script>
        /* 
        slice
        substring
        substr
         */
        var str="hello world"
        console.log(str.slice(0,3)) // startIndex<=num<end  hel
        console.log(str.substring(0,3))   //hel
        console.log(str.substr(0,4))      //hell
    </script>

4.修改()

1.split()

2.replace()

    <script>
        /* split 可以将字符串分割为数组 */
        var str="hello";
        var arr=str.split("1")
        console.log(arr)  //["hello"]
        console.log(str.replace("l","g"))
    </script>

5.综合

    <script>
        var str="let's go home";
        /* s'tel og emoh */
        /* 1.将字符串分割为数组 */
        /* ["let's","go","home"] */
        /* 2.遍历使数组每一项分割为数组 */
        /* [[l,e,t,',s],[g,o],[h,o,m,e]] */
        /* 翻转数组 */
        /* [[s,',t,e,l],[o,g],[e,m,o,h]] */
        /* join */
        /* ["s'tel","og ","emoh"] */
        /* s'tel og emoh  */
        var arr=str.split(" ");
        var all=[]
        arr.forEach(item=>{
            let i=item.split("").reverse().join("")
            all.push(i)
        })
        console.log(all.join(" "))  //s'tel og emoh
    </script>

    <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 */
/*         var arr=[]
            obj.forEach(item => {
            let name=item.name
            arr.push(name)
        })
        console.log(arr.join("/")) */
        var newArr=obj.map(item=>{
            return item.name
        })
        console.log(newArr.join("/"))  //汪峰/赵雷/房东的猫
    </script>

6.search

    <script>
        /* search 
        -1  字符串是不包含这个值
        startsWith
        */
        var str='hello world'
        var http="https://www.baidu.com"
        console.log(str.search("i"))   //-1
        console.log(http.startsWith("https"))  //true
    </script>

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

7.match

    <script>
        /* match 
        -->返回匹配的值，是一个数组
        replace()
        */
        var str="hello";
        console.log(str.match("e"))
        console.log(str.replace("l","g"))
    </script>