codie

JavaScript template engine specialized in generating JavaScript code

Codie

Codie is a simple JavaScript template engine specialized in generating code. Unlike other engines it really cares about newlines and indentation, allowing both the template and the generated code to be readable at the same time. You can use Codie to write tools such as compilers, template engines, various kinds of preprocessors or transformers — anything that produces more than a few lines of JavaScript.

Codie template looks like this:

#for i in list
  alert("Processing #{i}.");
  #if i % 2 == 0
    alert("#{i} is even.");
  #else
    alert("#{i} is odd.");
  #end
#end

With { list: [1, 2, 3] } as data, this template produces:

alert("Processing 1.");
alert("1 is odd.");
alert("Processing 2.");
alert("2 is even.");
alert("Processing 3.");
alert("3 is odd.");

Note that all alert calls are on the same indentation level (unlike in the template) because all indentation related to the #-commands is stripped.

$ npm install codie

Do not install Codie globally (using the -g option), otherwise you won’t be able to use the API.

Download the lib/codie.js file.

In Node.js, require the Codie module:

var Codie = require("codie");

In browser, include the Codie library in your web page or application using the <script> tag. Codie will be available in the Codie global object.

Using a template is a two-step process. First you need to compile the template text into a template function. Then you need to call this function with data to be filled into the template. Compiling saves time when you use the same template multiple times.

To compile a template, call the Codie.template method and pass the template text as a parameter. The method will return a template function or throw an exception if the template text is invalid:

var template = Codie.template('var #{name} = #{value};');

To fill the template, call the template function and pass an object with data. It’s properties will be available as variables in the template. The template function will return the filled template:

template({ name: "result", value: 42}); // Returns "var result = 42;".

To fill the template with different values, just call the template function again with a different data.

The template is a string with embedded expressions and commands. Any text which is not an expression nor a command is just copied verbatim to the output.

Expressions are just regular JavaScript expressions wrapped into #{ and }. They are evaluated and the result is emitted to the output.

Commands start with a # character at the beginning of a line, prefixed only by optional whitespace, and followed by the command name and parameters (if any) separated by whitespace.

The following commands are available:

Emits code in its body repeatedly, assigning values from an array to the loop variable sequentially.

#for i in list
  #{i}
#end

With { list: [1, 2, 3] } as data, this template produces:

1
2
3

All lines in the loop body are unindented by Codie.indentStep characters in the output. This is necessary to allow indentation to be used in the template and to make it disappear in the generated output.

Emits code in one of its branches depending on the condition.

#if i % 2 == 0
  alert("#{i} is even.");
#else
  alert("#{i} is odd.");
#end

With { i: 42 } as data, this template produces:

alert("42 is even.");

All lines in the loop body are unindented by Codie.indentStep characters in the output. This is necessary to allow indentation to be used in the template and to make it disappear in the generated output.

The #else branch is optional.

Evaluates its parameter, converts it to a string using the toString method, indents the result to the same level as the #block command and emits the result.

function foo() {
  #block body
}

With { body: "bar();\nbaz();" } as data, this template produces:

function foo() {
  bar();
  baz();
}

This command is useful mainly to combine parts of the generated output together.

For more details about the syntax see the source code.

Unindenting inside #if and #for commands removes Codie.indentStep characters from the beginning of lines. This property is set to 2 by default. You can modify it to use a different indentation level. Note that Codie does not care whether you use tabs or spaces for indentation.

Codie is designed to be extensible, so it’s easy to add new commands. All commands are described by descriptors stored in properties of the Codie.commands object. To add a new command, just add its descriptor there. See the implementation of other commands and the compileCommand function to get an idea how commands work.

I experimented with various means of delimiting. After a while I settled on line-oriented syntax with one-character delimiter. At that point, the "#" character won because it is easily recognizable, it’s not used in JavaScript, and commands prefixed by it resemble C preprocessor.

The only downside is that it is also used for interpolation in CoffeeScript. Should this be a problem, I’ll make the delimiter configurable.

Codie should run well in the following environments:

  • Node.js 0.6.6+
  • IE 8+
  • Firefox
  • Chrome
  • Safari
  • Opera

Codie is developed by David Majda (@dmajda). You are welcome to contribute code. Unless your contribution is really trivial you should get in touch with me first — this can prevent wasted effort on both sides. You can send code both as a patch or a GitHub pull request.