支持正則表達式的 String 對象的方法的其中replace()方法的用法
把aabb換成bbaa

var reg = /(\w)\1(\w)\2/g;
var str = "aabb";
console.log(str.replace(reg,"$2$2$1$1"));//"bbaa"
console.log(str.replace(reg,function($,$1,$2){
  return $2+$2+$1+$1;
}))

把the-first-name變成theFirstName

var reg = /-(\w)/g;
var str = "the-first-name";
var result = str.replace(reg,function($,$1){
  return $1.toUpperCase();
})
console.log(result)//"theFirstName"

正向預查，正向斷言

var str = "aabaaaa";
var reg = /a(?=b)/g;
str.match(reg);//a

正則簡單的去重

var str = "aaaabbbbbccccc";
var reg = /(\w)\1*/g;
console.log(str.replace(reg,"$1"));//abc

把"1000000000"變成"100.000.000"這種寫法，把后面往前面查，三位加個點

var str = "100000000";
var reg = /(?=(\B)(\d{3})+$)/g;
console.log(str.replace(reg,"."))//"100.000.000"