The original Canto constructor call

gistfile1.js

/**
* The constructor for the Canto class.
* This constructor is private and is not exported.  Use the canto() 
* factory function instead.
* @constructor
* @private
*/
function Canto(canvas) {
    if (!canvas.getContext)
        throw new Error("canto() requires a canvas element or id");

    // Store the 2D context that we wrap using the obscure property name _
    this._ = canvas.getContext("2d");
    resetCantoState(this);
}