Regular expression when reading files javascript

Question

I have a situation where I have 3 font files and I read its content in order to find mathes with font name. But the thing is that font names are Wingdings, Wingdings 2, Wingdings 3. And when I have Wingdings font name it matches all 3 files, but I need file that exactly is associated with font name, not all 3 of them. I tried to find it using indexOf method, but it didn't help. The only rational way is to use regular expression, but cannot think of a right one. One more thing need to be mentioned is that I have to pass a parameter into that regExp, something like

var regExp = new RegExp('\\^' + fontName + '$\\', 'g');
if (currentFileContent.search(regExp) !== -1) {...}

Any help will be greatly appreciated.

Try var regExp = RegExp('^' + fontName + '$'); if (regExp.test(currentFileContent)) { ... }. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Sep 30, 2015 at 18:46

Wiktor Stribiżew · Accepted Answer · 2015-09-30 20:19:16Z

4

It seems you try to use regex delimiters in a RegExp constructor. You only need /.../ in the literal notation.

Note you need not escape the start and end of string anchors, they lose their special meaning in the regex then. \\ matches a single \, but it cannot be matched after end of string ($).

Also, you can use RegExp#test() function to check if the string matches the pattern (note no g modifier can be used with it):

var regExp = RegExp('^' + fontName + '$'); 
if (regExp.test(currentFileContent)) { ... }

If font names contain special characters, use escapeRegExp function from MDN:

function escapeRegExp(string){
  return string.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
}

And then

var regExp = RegExp('^' + escapeRegExp(fontName) + '$');

And the final note: if the font names appear inside a larger string, and you need to match Windings but not Windings3, use

var regExp = RegExp('\\b' + escapeRegExp(fontName) + '\\b');

The \b is a word boundary.

UPDATE

To make sure you only match a font name that is not followed by a whitespace (if any) and a digit, use a (?!\\s*\\d) lookahead when declaring a RegExp:

var fontName = "Wingding";
var contents = "Font name: Wingding, the other file: Font name: Wingding 2. And so forth. ";
var rExp = RegExp(fontName + '(?!\\s*\\d)');
if (rExp.test(contents)) {
   document.write(fontName + " was found in '<i>" + contents + "</i>'.");
}

edited Sep 30, 2015 at 20:19

answered Sep 30, 2015 at 18:52

Wiktor Stribiżew

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9 Comments

Wiktor Stribiżew Over a year ago

Also, g makes no sense when you want to match a whole string with your regex.

Ivan Over a year ago

a tried, but it mathes all 3 files again. here may be the case where there's a space between Windings 3, not Windings3. and font name is just Windings. maybe check if there's characters after space?

Wiktor Stribiżew Over a year ago

Then just check for Windings, like /Windings(?!\s*\d)/.test(file).

Ivan Over a year ago

Sorry, but how can I pass a variable fontName instead of Windings string here?

Wiktor Stribiżew Over a year ago

Using RegExp: var regExp = RegExp(fontName + '(?!\\s*\\d)');

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