indexOf 查找字符串中某字符首次出现的位置

如果没出现结果，返回-1

let str = '2300dsklkladsklsdkl'
console.log(str.indexOf('s'))//5
console.log(str.indexOf('s2'))//-1

• https://www.cnblogs.com/djd66/p/15687745.html
• https://www.cnblogs.com/yegeng/p/12047880.html