1、字符串的方法

1-1 增加

1-1-1 concat 拼接

var a = 'hello'
var b = "world"
console.log(a.concat(b));

1-2 查询

1-2-1 slice(startIndex,endIndex)

1-2-2 substr(index,length)

注意：第二个参数 为长度

1-2-3 substring(startIndex,endIndex)

var arr = "hello"
console.log(arr.slice(0)); // hello
console.log(arr.slice(0,3)); // hel
console.log(arr.substr(0,3)); // hel
console.log(arr.substring(0,2)); // he

1-2-4 charAt(index) 根据下标查找对应的值

var str = "hello"
console.log(str.charAt(1)); // e

1-2-5 indexOf(value) 根据值查找对应的下标

var arr = "hello";
console.log(arr.indexOf('e')); // 1

1-2-6 includes 是否包含某位(多位)字符

var arr = "hello"
console.log(arr.includes("eh")); //false

1-3 length 字符串的长度

var str = "hello"
console.log(str.length);
var s = "故事的结尾，心上人"
console.log(handleStr(s));
function handleStr(value){
  if(value.length>5){
    return value.slice(0,5)+"..."
  }
  return value
}

1-4 其他方法

1-4-1 split(sperate)

• 把一个字符串分割成字符串数组

                var str = "hello";
        console.log(str.split());//["hello"]
        *console.log(str.split(""));//["h" "e" "l" "l" "o"] 以""来分割
        console.log(str.split("e"));//["h" "llo"]

             //"hello"取反输出        
                var str = "hello";
        var arr = str.split("");//字符串数组
        arr.reverse();
        var s = arr.join("");//字符串
        console.log(s);//olleh

       var arr = [1,2,3,4,5,6,7,8,9];
        var sum = [];
        //slice(startIndex,startIndex+3)
        for(var i=0; i<arr.length; i+=3){
            var res = arr.slice(i,i+3);
            // console.log(res);
            sum.push(res);
        }
        console.log(sum); //[[1,2,3],[4,5,6],[7,8,9]]

  1-4-2 search()

• search 返回值的下标,没有返回-1,和indexOf类似

        var str = "ywuie";
        var index = str.search("i");//3
        console.log(index);
        console.log(str.indexOf("i"));//3

  1-4-3 match()

• match返回匹配的字符，返回一个数组

        var str = "hello";
        var arr = str.match("l");
        console.log(arr);//["l", index: 2, input: "hello", groups: undefined]

  1-4-4 replace()

• replace()可以替换字符

        var str = "hello";
        console.log(str.replace("l",""));//helo

  1-4-5 trim() 去除字符串前后的空格

  // 正则表达式：  /^\s+|\s+$/g  
  var str = "   hello   ";
  var arr = []
  arr.push(str.trim())
  console.log(arr)

  // 正则表达式：  /^\s+|\s+$/g  
  var str = "   hello   ";
  var arr = []
  arr.push(str.trim())
  console.log(arr)