There is a super simple method 234234..toLocaleString()

I guess you want to realize the digit display of numbers. You want "12345" to be displayed as "12,345" instead of "123,45". Some people got it wrong.
The solution given by some people is that the number "123456" will be output as ",123,456", which obviously has an extra comma. My method will not have this problem.

1L's answer (useNumberObject.toLocaleString(), convert the numbers to strings, and use the local number format sequence.) can solve the problem, but it is not recommended because it depends on your local preferences and the results may be different for different people.

Implemented in a non-recursive way

Also supports decimal points!

"12345".split('').reverse().join('').replace(/(\d{3})\B/g,',').split('').reverse().join(''); //输出 12,345 "123456789".split('').reverse().join('').replace(/(\d{3})\B/g,',').split('').reverse().join(''); //输出 123,456,789 "1234567.89".split('').reverse().join('').replace(/(\d{3})\B/g,',').split('').reverse().join(''); //输出 1,234,567.89

Recursively implemented

This question requires recursive implementation, so the answer also provides recursive implementation.

//只处理整数 function addComma(str, currentIndex, result) { if (currentIndex === undefined) { currentIndex = str.length - 1; } if (result === undefined) { result = ''; } if (currentIndex < 0) { return result; } result = str.charAt(currentIndex) + result; if ((str.length - currentIndex) % 3 == 0 && currentIndex != 0) { result = "," + result; } return addComma(str, currentIndex - 1, result); } var n = '123456'; var output = addComma(n); console.log(output); //输出123,456 //带小数的处理示例 var n = '123456.78'; var output = addComma(n.split('.')[0]) + '.' + n.split('.')[1]; console.log(output); // 输出 123,456.78

The one upstairs is better

function get(num) { num = num.split('').reverse().join('') return num.match(/\d{1,3}/g).join(',').split('').reverse().join('') }

function addComma(str) { if(str.length <= 3) { return str; } var res = str.split(""); var resStr = res.splice(0, 3); return resStr.join("") + "," + addComma(res.join("")); }

'2342342323'.match(/\d{1,3}/g).join(',') // -> 234,234,232,3

The shortest code is here, let’s see if there is any shorter one.

From left to right

function myFunc(str) { return str.split('').reverse().join('').replace(/\B(?=(?:\d{3})+\b)/g, ',').split('').reverse().join('') }

From right to left

function myFunc(str) { return str.replace(/\B(?=(?:\d{3})+\b)/g, ',') }

(234234+"").replace(/\B(?=(\d{3})+(?!\d))/g, ",")

Someone asked this question a few days ago /q/10...
However, the above method is not suitable for decimal points. Since js does not support reverse pre-checking, use another set of regular rules for decimal points.

(234234.23132+"").replace(/\B(?=(\d{3})+(?=\.))/g, ",")

And what the hell is recursion? You don’t need to use recursion for this, right?

comdify : function (n){ 　　var re=/\d{1,3}(?=(\d{3})+$)/g; 　　var n1 = String(n).replace(/^(\d+)((\.\d+)?)$/,function(s,s1,s2){return s1.replace(re,"$&,")+s2;}); 　　return n1; }