080-engine-coffeescript.md

Using CoffeeScript with knitr

First we set a flag -p for the coffee engine to print the JavaScript output instead of evaluating the code (engine.opts = '-p'):

You need to install coffee, the command-line version of CoffeeScript.

CoffeeScript compiles javascript:

@square = (x) -> x * x

// (function() {
//   this.square = function(x) {
//     return x * x;
//   };
// 
// }).call(this);

To use CoffeeScript in an HTML document, use results="asis", echo=FALSE, and wrap the chunk in <script> tags.

@square = (x) -> x * x
@cube   = (x) -> square(x) * x

p = document.createElement("p");
p.appendChild(document.createTextNode("The cube of 3 is " + cube(3)))
document.body.appendChild(p)

<script type="text/javascript"> (function() { this.square = function(x) { return x * x; }; this.cube = function(x) { return square(x) * x; }; }).call(this); (function() { var p; p = document.createElement("p"); p.appendChild(document.createTextNode("The cube of 3 is " + cube(3))); document.body.appendChild(p); }).call(this); </script>

Of course you can also run the code, if you remove the -p flag from the chunk option engine.opts (I'm not evaluating this code chunk here because I do not have a proper version of coffee on Debian yet; if you do, you can remove eval=FALSE):

x = 42
console.log "The answer is ", x