Construction of a constrained point

A point can depend on another geometric object. This dependence can be given by using JavaScript syntax or by using GEONExT syntax. Here is an example using GEONExT syntax. The point A is draggable. The point B depends on point A: Its y-coordinate is set to 1 and its x-coordinate is set to the x-coordinate of A.

var b = JXG.JSXGraph.initBoard('jxgbox1', {originX: 40, originY: 100, unitX: 40, unitY: 40});
var free = b.createElement('point',[0,0], {name:'A', style:5});
var dep = b.createElement('point',["X(A)",1], {name:'B', style:8});

Now we do exactly the same with JavaScript syntax.

var b2 = JXG.JSXGraph.initBoard('jxgbox2', {originX: 40, originY: 100, unitX: 40, unitY: 40});
var free = b2.createElement('point',[0,0], {name:'A', style:5});
var dep = b2.createElement('point',[function(){ return free.X();}, 1], {name:'B', style:8});

The JavaScript syntax is much more robust against changes of the construction, but of course it looks more complicated. Lets look at it again in detail: First we construct a free, draggable point called free.

var free = b2.createElement('point',[0,0], {name:'A', style:5});

Then we construct the dependend point dep.

var dep = b2.createElement('point',[function(){ return free.X();}, 1], {name:'B', style:8});

The first coordinate of dep is given as an anonymous function:

function(){ return free.X();}

This function returns the x-coordinate of the point free.