1. 匹配最後兩位替換為00

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

   2.手機號中間4為替換為 *

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

2. 匹配手機號

    let phone ="17700001234"
    let telReg =/^[1][3-9][0-9]{9}$/;
     let reg_tel =/^[1][3-9]\d{9}$/;
    if (telReg.test(phone)) {
    alert(true)
    }else{
      alert(false)
    }
     

   4.正整數

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

   5.正數負數浮點數

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

   6.去掉文件後綴

   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;
    }
   }

3. 匹配小於等於5的數

    var RegExp=/(^([0-4])(\.[0-9])?$)|(^5$)/;
    var reg = /^5$|^(\[0-4])(\.\d+)*$/

4. 匹配中文

   var reg = /[\u4E00-\u9FA5]/

5. 匹配字母數字中文

   /^[a-zA-Z0-9\u4E00-\u9FA5]+$/

   10.大於0小於40的正整數

   const regs = /^([1-9]|[1-3]\d|40)$/
   
   console.log(regs.test(輸入的值));

6. 0-100 保留4位小數

    var reg1 = /^(0\.[1-9][0-9]{0,3}|[1-9][0-9]?(\.[0-9]{1,4})?)$/

Mozilla 正則表達式