How do I know if a replacement has occurred in a Javascript replace function?
I have a function that scans a series of lines and replaces them:
var nam = 'Here is a sample string 1/23';
var d = new Date();
var mon = d.getMonth()+1;
var day = d.getDate();
nam = nam.replace(/\d{1,2}\/\d{1,2}/,day+'/'+mon);
However, if no replacements are made (because no regex was found in the string), I want to append day+'/'+mon
to the end of the string.
How can I find out the number of matches of regular expressions?
You have several options.
You can check the match first before doing the replacement, but replacing it means re-evaluating the regex, which, depending on the regex, can be quite expensive:
var re = /\d{1,2}\/\d{1,2}/;
if (re.test(nam))
nam = nam.replace(re, day+'/'+mon);
else
nam += day+'/'+mon;
Or, as mentioned in the comments, you can replace the string and compare it to the original string - you just need to put it in a temporary variable that costs almost nothing:
var temp = nam.replace(/\d{1,2}\/\d{1,2}/, day+'/'+mon);
if (temp == nam)
nam += day+'/'+mon;
else
nam = temp;
You can check it first:
nam = /\d{1,2}\/\d{1,2}/.test(nam) ? nam.replace(/\d{1,2}\/\d{1,2}/,day+'/'+mon) : nam + day+'/'+mon;
If you want to know if it was replaced and not which part:
temp_nam = nam.replace(/\d{1,2}\/\d{1,2}/,day+'/'+mon); replaced = (temp_nam == nam) ? false : true; --- more code --- nam = temp_nam;
Just store the replaced string in a temporary variable and write it after checking in a real variable.