browserify-transform-tools

This package contains tools for helping you write transforms for browserify.

Many different transforms perform certain basic functionality, such as turning the contents of a stream into a string, or loading configuration from package.json. This package contains helper methods to perform these common tasks, so you don't have to write them over and over again:

• makeStringTransform() creates a transform which consumes and returns a string, instead of using a stream.
• makeFalafelTransform() parses a JS file using falafel and allows you to modify the code.
• makeRequireTransform() passes you the contents of each require() call in each script, and allows you to rewrite the require statement.
• All of the above will automatically search for transform configuration in package.json and pass it to you if available, but if you have a more complicated use case than the make*Transform() functions will support, then loadTransformConfig() will load configuration for you.
• runTransform() can be used to unit test your shiny new transform.

Installation

Install with npm install --save-dev browserify-transform-tools.

Creating a String Transform

Browserify transforms work on streams. This is all well and good, until you want to call a library like "falafel" which doesn't work with streams. (If you're using falafel specifically, see below for makeFalafelTransform.)

Suppose you are writing a transform called "unbluify" which replaces all occurances of "blue" with a color loaded from a configuration:

var options = {excludeExtensions: [".json"]};
module.exports = transformTools.makeStringTransform("unbluify", options,
    function (content, transformOptions, done) {
        var file = transformOptions.file;
        if(!transformOptions.config) {
            return done(new Error("Could not find unbluify configuration."));
        }

        done null, content.replace(/blue/g, transformOptions.config.newColor);
    });

Notice that the color we replace "blue" with gets loaded from configuration. The configuration can either be specified in the project's package.json:

{
    "name": "myProject",
    "version": "1.0.0",
    ...
    "unbluify": {"newColor": "red"}
}

Or alternatively you can set the "unbluify" key to be a js or JSON file:

{
    "unbluify": "unbluifyConfig.js"
}

And then configuration will be loaded from that file:

module.exports = {
    newColor: "red"
};

Note this means you can use enviroment variables to make changes to your configuration.

Parameters for makeStringTransform():

• transformFn(contents, transformOptions, done) - Function which is called to do the transform. contents are the contents of the file. done(err, transformed) is a callback which must be called, passing the a string with the transformed contents of the file. transformOptions consists of:

  • transformOptions.file is the name of the file (as would be passed to a normal browserify transform.)
  • transformOptions.configData is the configuration data for the transform (see loadTransformConfig below for details on where this comes from.)
  • transformOptions.config is a copy of transformOptions.configData.config for convenience.

• options.excludeExtensions - A list of extensions which will not be processed. e.g. "['.coffee', '.jade']"

• options.includeExtensions - A list of extensions to process. If this options is not specified, then all extensions will be processed. If this option is specified, then any file with an extension not in this list will skipped.

Creating a Falafel Transform

Many transforms are based on falafel. browserify-transform-tools provides an easy way to define such transforms. Here is an example which wraps all array expressions in a call to fn():

var options = {};
// Wraps all array expressions in a call to fn().  e.g. '[1,2,3]' becomes 'fn([1,2,3])'.
module.exports = transformTools.makeFalafelTransform("array-fnify", options,
    function (node, transformOptions, done) {
        if (node.type === 'ArrayExpression') {
            node.update('fn(' + node.source() + ')');
        }
        done();
    });

makeFalafelTransform() will be called once for every node in your JS file. You can update the node. Be sure to pass errors back via done(err), and call done() when complete.

Options passed to makeFalafelTransform() are the same as for makeStringTransform(), as are the transformOptions passed to the transform function. You can additionally pass a options.falafelOptions to makeFalafelTransform - this object will be passed as an options object directly to falafel.

Creating a Require Transform

Many transforms are focused on transforming require() calls. browserify-transform-tools has a solution for this:

transform = transformTools.makeRequireTransform("requireTransform",
    {evaluateArguments: true},
    function(args, opts, cb) {
        if (args[0] === "foo") {
            return cb(null, "require('bar')");
        } else {
            return cb();
        }
    });

This will take all calls to require("foo") and transform them to require('bar'). Note that makeRequireTransform can parse many simple expressions, so the above would succesfully parse require("f" + "oo"), for example. Any expression involving core JavaScript, __filename, __dirname, path, and join (where join is an alias for path.join) can be parsed. Setting the evaluateArguments option to false will disable this behavior, in which case the source code for everything inside the ()s will be returned.

Note that makeRequireTransform expects your function to return the complete require(...) call. This makes it possible to write require transforms which will, for example, inline resources.

Again, all other options you can pass to makeStringTransform are valid here, too.

Loading Configuration

All make*Transform() functions will automatically load configuration for your transform and make it available via transformOptions.configData and transformOptions.config. If you are writing your own transform which doesn't use one of these functions, you can still use browserify-transform-tools to load configuration:

var transformTools = require('browserify-transform-tools');

var configData = transformTools.loadTransformConfig('myTransform', file, function(err, configData) {
    var config = configData.config;
    var configDir = configData.configDir;
    ...
});

loadTransformConfig() will search the parent directory of file and its ancestors to find a package.json file. Once it finds one, it will look for a key called 'myTransform' (taken from the transformName passed into loadTransformConfig().) If this key maps to a JSON object, then loadTransformConfigSync() will return the object. If this key maps to a string, then loadTransformConfigSync() will try to load the JSON or JS file the string represents and will return that instead. For example, if package.json contains {"myTransform": "./myTransform.json"}, then the contents of "myTransform.json" will be returned. configData.config is the loaded data. configData.configDir is the directory which contained the file that data was loaded from (handy for resolving relative path names.) For other fields returned by loadTransformConfigSync(), see comments in the source.

There is a synchronous version of this function, as well, called loadTransformConfigSync(transformName, file).

Note that since configuration can be supplied in a .js file, the .js file can alter the configuration based on environment variables.

Running a Transform

If you want to unit test your transform, then runTransform() is for you:

var myTransform = transformTools.makeFalafelTransform(...);
var dummyJsFile = path.resolve(__dirname, "../testFixtures/testWithConfig/dummy.js");
var content = "console.log('Hello World!');";
transformTools.runTransform(myTransform, dummyJsFile, {content: content},
    function(err, transformed) {
        // Verify transformed is what we expect...
    }
);

Thanks

Some of this was heavily inspired by:

• ForbesLindesay's rfileify
• thlorenz's browserify-shim