var num = 123456789; 
1.格式化为千分位输出 num.toLocaleString()
//"123,456,789" 
2.格式化为千分位带$符号输出 
num.toLocaleString("en-US",{style:"currency",currency:"USD"})
//"$123,456,789.00" 
3.格式化为带￥符号输出 
num.toLocaleString("zh-Hans-CN",{style:"currency",currency:"CNY"})
//"￥123,456,789.00"