Bounding box
The bounding box defines the viewport of the board, i.e. the portion of the $\mathbb{R}^2$ that is shown. The JavaScript code
~~~
var board = JXG.JSXGraph.initBoard('jxgbox', {
boundingbox:[-5,10,5,-2],
keepaspectratio: true,
axis:true
});
~~~
sets the vertical and horizontal units and the position of the origin such that the upper left corner of the drawing panel has coordinates $(-5,10)$ and the lower right corner of the drawing panel has coordinates $(5,-2)$.
// Define the id of your board in BOARDID
var board = JXG.JSXGraph.initBoard(BOARDID, {
boundingbox: [-5, 10, 5, -2],
axis: true
});