function parseNum(num) { return num.toString().replace(/(?=(?!\b)(\d{3})+$)/g, ',')}
1. (?=pattern) 正向肯定预查(look ahead positive assert)
2. (?!pattern) 正向否定预查(negative assert)
function parseNum(num) { return num.toString().replace(/(?=(?!\b)(\d{3})+$)/g, ',')}
1. (?=pattern) 正向肯定预查(look ahead positive assert)
2. (?!pattern) 正向否定预查(negative assert)