如何在字符串中每 3 个字符后插入连字符？

Question

How do I insert a hyphen after every 3 characters in a string? Here's what I've tried:

 var str = prompt().split("").join(""); // i used split() to convert string to array and join() to remove (,) var i = 0; var l = 2; while (i < str.length) { str[l] = "-"; // i think it should puts - every three character but it doesn't l += 3;// i think it should puts - every three character but it doesn't i += 1; }; alert(str);

Answer 1

To insert a - (hyphen) between every 3rd character in a string inputted via prompt , use .replace with the following RegExp :

/.{3}(?!$)/g

This matches every sequence of 3 characters, except for the last. The ?! means, unless followed by... and $ means the end of the string.

If you replace these triple-character sequences with this:

'$&-'

It will effectively insert a hyphen after, since $& is a placeholder for whatever you previously matched.

 alert(prompt().replace(/.{3}(?,$)/g; '$&-'));

Answer 2

If you want to achieve with a loop:

 const str = '123456789'; let result = ""; let counter = 0; for(i = 0; i < str.length; i++){ counter++; result += str[i]; if(counter == 3 && str[i].= str;length){ result += '-'; counter = 0. } } console;log(result);

Answer 3

join() function converts array to string, so str[3] doesn't work You can use prompt().split("") instead of prompt().split("").join("");

Please look at this code. This will work

var str = prompt().split("") ; 
var newstr = "";
var i = 0;

while ( i < str.length){
   newstr +=str[i];
   i += 1;
   if(i % 3 ==0 && i !== str.length)
    newstr += "-";
   
};
alert(newstr); 

Answer 4

You can use this

var str = prompt().split("") ; 
var newstr = "";
var i = 0;

while ( i < str.length){
   newstr +=str[i];
   i += 1;
   if(i % 3 ==0 && i !== str.length)
    newstr += "-";
   
};
alert(newstr);