1. string.search()

返回值：匹配成功的第一个字符的下标，未匹配则返回-1

用法：string.search(searchValue)

举个例子：

 let searchVal = 'yyds'
 let searchResult = searchVal.search('y')
 console.log(searchResult) // 0  

3. string.includes()

返回值：Boolean

用法： string.includes(searchValue, start) 第二个参数从是指定下标开始查找

举个栗子：

 let searchVal = 'yyds'
 let searchResult = searchVal.includes('y', 1)
 console.log(searchResult) // true

4. string.indexOf()

返回值：匹配成功的第一个字符的下标，未匹配则返回-1

用法：string.indexOf(searchValue, start)

栗子：

let searchVal = 'yyds'
let searchResult = searchVal.indexOf('y', 0)
console.log(searchResult) // 0 

5. string.lastIndexOf()

和indexOf()的区别，从字符串的尾部开始查找

返回值：匹配成功的第一个字符的下标，未匹配则返回-1

用法：string.indexOf(searchValue, start)

栗子：

let searchVal = 'yyds'
let searchResult = searchVal.lastIndexOf('y')
console.log(searchResult) // 1