function.md

node-basic documentation

Adding a function or constant

In node-basic, functions and constants are actually the same thing. A constant can be defined as a set value or a function. Most functions are contained in the lib/functions folder, and all of the constants and some miscellaneous functions are in the lib/executor. For this tutorial, we will create a function that gets the screen aspect ratio in the float:1 format, where float is returned.

Open the graphics.js file in lib/functions. This file contains many graphics functions, such as ScreenWidth and ScreenHeight. At the bottom of the file, add the following code:

/**
 * Gets the current aspect ratio, in float:1 format, where float is returned
 * 
 * @returns {number}
 */
exports.aspect = function() {
};

Here we create the basic function. The function name should always be lowercase. Any arguments provided to the function will be passed as the function arguments, and the function should return the result. The function context (the value of this inside the function) will be the current execution context.

Since this functions needs to access the width and height of the canvas, we will have to use the draw IOInterface again. This has already been imported as the ctx variable in this file, so we are ready to write the function.

var result = 0;
ctx.read(function(response, cancel) {
	if (response.command !== 'screensize') return;
	cancel();
	result = response.data.width / response.data.height;
});
ctx.write({ command: 'screensize' });
return result;

Whats going on here?? Well, we've seen one part of this before. The write function call is exactly the same as the one in the adding a command guide, except without the arguments parameter.

Some commands, in this case screensize, send a response back to node-basic through the IOInterface. These responses are still synchronous, though, so any handlers added through the read function will still be executed before returning. Here, we first make sure that the response is from the screensize command, and then cancel the handler. This prevents the handler being called for any future screensize commands. We then set the result variable to the ratio, and return it.

We need to add the read handler before we call write because the write call is synchronous.

There we go! Now, open up node-basic in a graphical environment, and try out your new function!