1. slice()

slice(startIndex,endIndex)

2. substr()

substr(index,length)

3. substring()

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

4. charAt()

charAt(index) 根据下标查找对应的值

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

5. indexOf(value)

根据值查找对应的下标 找不到返回-1

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

6. search(value)

根据值查找对应的下标 找不到返回-1

 var str = "你是谁"
 var index = str.search("她")
 console.log(index);   //  -1

7. includes

是否包含某位(多位)字符 返回boolean

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

8. match(value)

返回匹配的字符串，返回的是数组

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

9. 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
}