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

1-2-7 search(index)

var str="你是谁";
var index=str.search("是");
console.log(index);

1-2-8 match 匹配

var str="hello";
var arr=str.match("l");
console.log(arr);

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 trim()去除字符串前后的空格

var str="  hello  ";
var arr=[];
arr.push(str.trim());
console.log(arr);

1-5 replace()替换字符串中的元素

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

1-6 split()将字符串转换为数组

 var str="hello";
var arr=str.split("");//["h", "e", "l", "l", "o"]

1-7 判断开始结束 返回boolean

var str="武汉";
console.log(str.startsWith("武"));
console.log(str.endsWith("汉"))