Replace typeof var !== "undefined" in file using JavaScript

replace_typeof_undefined.js

fs = require('fs')

var file = process.argv[2];

function replaceAll(str, needle, replacement) {
    return str.split(needle).join(replacement);
}

console.log("Processing file " + file);

fs.readFile(file, 'utf8', function (err,data) {
	if (err) {
		return console.log(err);
	}
	
	var equalsUntitledMatches = data.match(/typeof [0-9a-zA-Z\[\]\.]* [!=]== \"undefined\"/g);
	
	//console.log(JSON.stringify(equalsUntitledMatches, null, 4));
	

	for (var i = 0; i < equalsUntitledMatches.length; i++) {
		var before = equalsUntitledMatches[i];
		
		var variableRegex = new RegExp(/typeof ([0-9a-zA-Z\[\]\.]*) ([!=]==) \"undefined\"/g);
		var variableMatches = variableRegex.exec(before);				

		var operator = variableMatches[2];
		if(operator === "!==")
		{
			var after = "!isNull("+variableMatches[1]+")";
		}
		else if(operator === "===")
		{
			var after = "isNull("+variableMatches[1]+")";
		}
		else
		{
			throw new Error("Unrecognised operator "+ operator +" found at file: ")
		}
		
		console.log(before +"   ======>   "+ after);
		
		data = replaceAll(data, before, after);
	}
	
	console.log(data);
});