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Bearing (bidirectional communication)
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<iframe 
    src="https://jsxgraph.org/share/iframe/bearing-bidirectional-communication" 
    style="border: 1px solid black; overflow: hidden; width: 550px; aspect-ratio: 55 / 65;" 
    name="JSXGraph example: Bearing (bidirectional communication)" 
    allowfullscreen
></iframe>
This code has to 
<input type="text" id="degrees">
<button onclick="setDirection()">set direction</button>

<div id="board-0-wrapper" class="jxgbox-wrapper " style="width: 100%; ">
   <div id="board-0" class="jxgbox" style="aspect-ratio: 1 / 1; width: 100%;" data-ar="1 / 1"></div>
</div>

<script type = "text/javascript"> 
    /*
    This example is licensed under a 
    Creative Commons Attribution 4.0 International License.
    https://creativecommons.org/licenses/by/4.0/
    
    Please note you have to mention 
    The Center of Mobile Learning with Digital Technology
    in the credits.
    */
    
    const BOARDID = 'board-0';

    const board = JXG.JSXGraph.initBoard(BOARDID, {
        axis: true,
        boundingbox: [-2, 1.5, 2, -1.5],
        keepaspectratio: true
    });
    var c = board.create('circle', [
        [0, 0], 1
    ], {fixed:true});
    var g = board.create('glider', [-1, 0.5, c], {
        name: 'drag me'
    }); // global variable
    var p0 = board.create('point', [1, 0], {visible: false});
    var p1 = board.create('point', [0, 0], {visible: false});
    var a = board.create('angle', [p0, p1, g], {withLabel: false, radius: 0.35});
    g.on('drag', function() {
        document.getElementById('degrees').value = (Math.atan2(g.Y(), g.X()) * 180 / Math.PI).toFixed(0);
    });
    
    var setDirection = function() {
        var phi = 1 * document.getElementById('degrees').value * Math.PI / 180.0;
        var r = c.Radius();
        g.moveTo([r * Math.cos(phi), r * Math.sin(phi)], 1000);
    
    }
 </script> 
/*
This example is licensed under a 
Creative Commons Attribution 4.0 International License.
https://creativecommons.org/licenses/by/4.0/

Please note you have to mention 
The Center of Mobile Learning with Digital Technology
in the credits.
*/

const BOARDID = 'your_div_id'; // Insert your id here!

const board = JXG.JSXGraph.initBoard(BOARDID, {
    axis: true,
    boundingbox: [-2, 1.5, 2, -1.5],
    keepaspectratio: true
});
var c = board.create('circle', [
    [0, 0], 1
], {fixed:true});
var g = board.create('glider', [-1, 0.5, c], {
    name: 'drag me'
}); // global variable
var p0 = board.create('point', [1, 0], {visible: false});
var p1 = board.create('point', [0, 0], {visible: false});
var a = board.create('angle', [p0, p1, g], {withLabel: false, radius: 0.35});
g.on('drag', function() {
    document.getElementById('degrees').value = (Math.atan2(g.Y(), g.X()) * 180 / Math.PI).toFixed(0);
});

var setDirection = function() {
    var phi = 1 * document.getElementById('degrees').value * Math.PI / 180.0;
    var r = c.Radius();
    g.moveTo([r * Math.cos(phi), r * Math.sin(phi)], 1000);

}
This is an example of _bidirectional communication_ of JSXGraph with other elements of the web page. 1. One can type a new value for the angle into the text box and 2. see the actual value of the angle in the same text box when dragging the glider. 
<input type="text" id="degrees">
<button onclick="setDirection()">set direction</button>
// Define the id of your board in BOARDID

const board = JXG.JSXGraph.initBoard(BOARDID, {
    axis: true,
    boundingbox: [-2, 1.5, 2, -1.5],
    keepaspectratio: true
});
var c = board.create('circle', [
    [0, 0], 1
], {fixed:true});
var g = board.create('glider', [-1, 0.5, c], {
    name: 'drag me'
}); // global variable
var p0 = board.create('point', [1, 0], {visible: false});
var p1 = board.create('point', [0, 0], {visible: false});
var a = board.create('angle', [p0, p1, g], {withLabel: false, radius: 0.35});
g.on('drag', function() {
    document.getElementById('degrees').value = (Math.atan2(g.Y(), g.X()) * 180 / Math.PI).toFixed(0);
});

var setDirection = function() {
    var phi = 1 * document.getElementById('degrees').value * Math.PI / 180.0;
    var r = c.Radius();
    g.moveTo([r * Math.cos(phi), r * Math.sin(phi)], 1000);

}

license

This example is licensed under a Creative Commons Attribution 4.0 International License.
Please note you have to mention The Center of Mobile Learning with Digital Technology in the credits.