I would very much appreciate some assistance from the munity on replacing a string at xth position intervals, using javascript regex. For example, if the string length is 161 and the replacement text is <br />, regex would replace the string at the 40th, 80th, 120th, and 160th positions with this replacement text. Is this possible using regex?

Thank you very much.

I would very much appreciate some assistance from the munity on replacing a string at xth position intervals, using javascript regex. For example, if the string length is 161 and the replacement text is <br />, regex would replace the string at the 40th, 80th, 120th, and 160th positions with this replacement text. Is this possible using regex?

Thank you very much.

• javascript
• regex
• string
• replace
• position

Share Follow edited Oct 28, 2011 at 14:52 user717236 asked Oct 28, 2011 at 14:49 user717236user717236 5,0392020 gold badges6767 silver badges102102 bronze badges 4

• 1 While it may be possible with regex, why not use other techniques to do this? It seems to me that you want to insert something every (n % 40 == 0) position. – FailedDev Commented Oct 28, 2011 at 14:53
• Yes, that is correct. Why not other techniques? Because my logic thinks regex would require less lines of code and could be the simplest. I'm open to other techniques, however. – user717236 Commented Oct 28, 2011 at 14:54
• 1 Less lines of code doesn't necessarily make it neither simpler nor more efficient. Just a thing to note. – FailedDev Commented Oct 28, 2011 at 14:59
• Yes, thank you, I appreciate your advice. Note: That's why I said 'could' and not 'will' in my above ment. – user717236 Commented Oct 28, 2011 at 15:03

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 4

A method to add <br /> at ever 40th position is by using the following line:

string = string.replace(/([\S\s]{40})/g , "$1<br />");

If you want to dynamically set the position use:

var positions = 40;
var pattern = new RegExp("([\\s\\s]{" + positions + "})", "g");
string = string.replace(pattern , "$1<br />");

Explanation of the code:

1. The first argument of the replace function is a RegExp:
   • ([\S\s] = all non-whitespace and white-space characters = every character).
   • {40} = 40 characters
   • The g flag means: global match, ie: match every possible occurence
   • The parentheses inside the RegExp means: Create a group. This group can later be referred by $1 (first group)
2. The second argument of the replace function contains $1<br />. That is: replace the full match by the first group ($1), and add <br /> to it.

var str = "12345678901234567890";
var newStr = str.replace(/(.{5})/g,"$1<br/>");

for every 40, change the 5 to 40.