js实现千位分隔符

[chess99]

var result = "123456789".replace(/(?=(\B\d{3})+$)/g, ",");
console.log(result);
// => "123,456,789"

[9a-aaaaaaaa]

var result = "123456789".replace(/(?=(\B\d{3})+$)/g, ",");
console.log(result);
// => "123,456,789"

@chess99

const regEx = /(?!^)(?=(\d{3})+$)/g; 这样子也可以