rhubarb

Conditional compilation tool for javascript

Barbarian way to make custom builds

What does it do?

It takes the source code

if (Whatever.hasFeature("foo")){
	doFunctionFoo();
} else {
	console.log("I haven't feature foo!");
}

if (__environment !== 'production'){
	console.debug("I'm in debug environment");
}

and the state

{
	"Whatever": {
		"hasFeature": function(feature){
			if (feature === 'foo'){
				return true;
			}
		}
	},
	"__environment": "Dark basement"
}

and returns following:

if (true){
	doFunctionFoo();
} else {
	console.log("I haven't feature foo!");
}

if (true){
	console.debug("I'm in debug environment");
}

What this stuff doesn't do?

This is not a minifier/compressor. It just inlines constants.

This is not a dead code removal tool. There are some expression computations, but Rhubarb doesn't touch block statements. I would like to drop if branches if the condition was calculated, but found that this apparently simple feature is actually tricky and error-prone.

Why not UglifyJS?

UglifyJS2 is a great compression tool with conditional compilation. Unfortunately, it cannot always guess if expression evaluates constant value.

This tool can. With your little help.

And you can use functions/methods!

How to use it?

Currently it only can be used as a module.

There's only one method, inline with following signature:

require("rhubarb").inline(code, state [, options]);

• code is a javascript code.

• state is an object that is used as global. If state has (in javascript operator is used) value, it is used for replacement. If it hasn't, code stays the same.

• options is an optional object with options:

Options

options.scope

Described the way identifiers are resolved into variables.

• global (default) - only global variables (and its properties) are replaced.
• flat - variables are replaced everywhere, even if there's a local variables with same name
• undeclared - same as global, but if a global variable was defined (for example, with var), it is skipped

Uncomputables

Sure, we cannot prceisely define all the state at the build time.

There's a special object UNCOMPUTABLE exported from module. If any variable, property or function result equals to UNCOMPUTABLE, it will be ignored.

There's no need to assign this value of all properties, if state or any its descendant properties was not defined (hasOwnProperty in JavaScript), it's assumed to be uncomputable. This approach doesn't work for function calls. If you're going to return an object, make sure all uncomputable properties are marked explicitly.