Question

I wrote some regexp. It works when I execute it with string typed in console, but not in some cases in my script.

Here is my console output:

>body
["VERSION:2.1", "N:;S Wicius;;;", "FN:S Wicius", "TEL;PREF;CELL:000000000"]
>records.line
/^([^:;]+)(?:;([^:]+))?:(.+)$/gm
>records.line.exec( body[1] )
null
>body[1] == "N:;S Wicius;;;"
true
>records.line.exec( "N:;S Wicius;;;" )
["N:;S Wicius;;;", "N", undefined, ";S Wicius;;;"]

>for( var i = 0; i < body.length; i++ ) {
  var line = [];
  if( line = records.line.exec( body[i] ) )
    console.log( line )
}
["VERSION:2.1", "VERSION", undefined, "2.1"]
["FN:S Wicius", "FN", undefined, "S Wicius"]

Answer 1

Well, the problem is caused by the combination of the following factors:

1. records.line is the same object in each iteration
2. regex is defined with /g modifier and
3. exec method changes lastIndex property of your regexp object

lastIndex is a read/write property of RegExp objects. For regular
expressions with the “g” attribute set, it contains an integer that
specifies the character position immediately following the last match
found by the RegExp.exec( ) and RegExp.test( ) methods. These methods
use this property as the starting point for the next search they
conduct.

This property allows you to call those methods repeatedly, to
loop through all matches in a string and works only if the “g”
modifier is set.

You can fix the issue by changing any of these 3 conditions (you also could manually reset records.line.lastIndex = 0 in each iteration). Your /g modifier seems to be useless, so just get rid of it.