正则表达式

1. 匹配最后两位替换为00

let str= "123456" ;
 str.replace(/\d{2}$/, '00');    // 123400
str.replace(/(\d{4})(\d{2})/, '$100');   // 123400

2.手机号中间4为替换为 *

let str ="17700001234"
str.replace(/(\d{3})\d{4}(\d{4})/,'$1***$2') //177****1234

3. 匹配手机号

    let phone ="17700001234"
    let telReg =/^[1][2-9][0-9]{9}$/;
    if (telReg.test(phone)) {
    alert(true)
    }else{
      alert(false)
    }
  

4.正整数

let reg = /^[1-9]\d*$/

5.正数负数浮点数

let reg = /^(\-|\+)?\d+(\.\d+)?$/ 

6.去掉文件后缀

function splitFileName(text) {
    var pattern = /\.{1}[a-z]{1,}$/;
    if (pattern.exec(text) !== null) {
        return (text.slice(0, pattern.exec(text).index));
    } else {
        return text;
    }
}