symdiff plugins are pure functions that transform a string into an array of strings. The input is the file content, the output the classes used in the file.


Take for instance CSS, you could do it like this naively:

module.exports = 
    function symdiffCSS(cssString) {
        return cssString
                // take everything of the form .abcd
                // remove leading dot
                .map(function(clazz) {
                    return clazz.substring(1);

…but please don’t and use a parser instead.

Error Handling

With a symdiff plugin there are no errors, semantically. Either it detects classes in a string or it doesn’t and it the latter case it should just return an empty array. (Even if the file is syntactically invalid.) Never should a plugin throw.


Put them in an array and attach it to the warnings property of the array you return like this:

module.exports = 
    function symdiffHTML(htmlString) {
        var classes = [],
            warnings = [];

        // business logic here
        warnings.push("ng-class not supported yet!");
        // more business logic

        classes.warnings = warnings;
        return classes;