将数字转换为千分位

1.正则表达式的方式

let str = '4000'
let string = "1234567"
str.replace(/(\d{1,3})(?=(\d{3})+$)/g,function($1){
    return $1=$1+','
})
string .replace(/(\d{1,3})(?=(\d{3})+$)/g,function($1){
    return $1=$1+','
})
结果为4,000     1,234,567

2.正则表达式的方式

let str = '4000'
let string = "1234567"
str.replace(/\d{1,3}(?=(\d{3})+$)/g,function(s){
    return s+','
}) 
string .replace(/\d{1,3}(?=(\d{3})+$)/g,function(s){
    return s+','
}) 
结果为4,000     1,234,567