JavaScript: Insert a character after every N characters

I have a string, which always has a lenght of 32:

var str = "34v188d9cefa401f988563fb153xy04b";

Now I need to add a minus (-) after following number of characters:

• First minus after 8th character
• Second minus after 12th character
• Third minus after 16th character
• Fourth minus after 20th character

Output should be:

34v188d9-cefa-401f-9885-63fb153xy04b

So far I have tried different calculations with e.g.:

str.split('').reduce((a, b, c) => a + b + (c % 6 === 4 ? '-' : ''), '');

But I don’t get the expected result.

>Solution :

You could use a regex replacement:

var str = "34v188d9cefa401f988563fb153xy04b";
var output = str.replace(/^(.{8})(.{4})(.{4})(.{4})(.{12})$/, "$1-$2-$3-$4-$5");
console.log(output);