javascript如何方便地对一个数字进行千位分隔？

Question

比如1000转化成1,000
99999转化成99,999

Answer 1

找到了，自问自答一下
Number(123456).toLocaleString()

Answer 2

const formatNumber = (num)=> {  
    const reg=/\d{1,3}(?=(\d{3})+$)/g;   
    return (num + '').replace(reg, '$&,');  
}

Answer 3

function _String (data) {
  return data == null ? '' : String(data)
}

// thousands(1234567) => 1,234,567
function thousands (str, symbol) {
  symbol = symbol || ','
  return _String(str).replace(/([^.]*)?(\.)?(.*)?/, function(item, pre, dot, next) {
    return _String(pre).replace(/(.(?=(.{3})+$))/g, '$1' + symbol) + _String(dot) + _String(next)
  })
}