# Difference between revisions of "Even simpler function plotter"

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### The underlying JavaScript code

<input type="text" id="input" value="sin(x)*x">
<input type="button" value="plot" onClick="plotter()">
<input type="button" value="clear all" onClick="clearAll()">
<input type="button" value="add tangent" onClick="addTangent()">
<input type="button" value="add Derivative" onClick="addDerivative()">

var board = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[-5,8,8,-5], axis:true});
var f, curve; // global objects

function plotter() {
var txtraw = document.getElementById('input').value;
f = board.jc.snippet(txtraw, true, 'x', true);
curve = board.create('functiongraph',[f,
function(){
var c = new JXG.Coords(JXG.COORDS_BY_SCREEN,[0,0],board);
return c.usrCoords[1];
},
function(){
var c = new JXG.Coords(JXG.COORDS_BY_SCREEN,[board.canvasWidth,0],board);
return c.usrCoords[1];
}
],{name:txtraw, withLabel:true});
var q = board.create('glider', [2, 1, curve], {withLabel:false});
var t = board.create('text', [
function(){ return q.X()+0.1; },
function(){ return q.Y()+0.1; },
function(){ return "The slope of the function f(x)=" + txtraw + "<br>at x=" + q.X().toFixed(2) + " is equal to " + (JXG.Math.Numerics.D(f))(q.X()).toFixed(2); }
],
{fontSize:15});
}

function clearAll() {
JXG.JSXGraph.freeBoard(board);
board = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[-5,8,8,-5], axis:true});
f = null;
curve = null;
}

function addSlopeInfo() {
if (JXG.isFunction(f)) {
var txtraw = document.getElementById('input').value;
board.suspendUpdate();
var q = board.create('glider', [2, 1, curve], {withLabel:false});
var t = board.create('text', [
function(){ return q.X()+0.1; },
function(){ return q.Y()+0.1; },
function(){ return "The slope of the function f(x)=" + txtraw + "<br>at x=" + q.X().toFixed(2) + " is equal to " + (JXG.Math.Numerics.D(f))(q.X()).toFixed(2); }
],
{fontSize:15});
board.unsuspendUpdate();
}
}

function addTangent() {
if (JXG.isFunction(f)) {
board.suspendUpdate();
var p = board.create('glider',[1,0,curve], {name:'drag me'});
board.create('tangent',[p], {name:'drag me'});
board.unsuspendUpdate();
}
}

function addDerivative() {
if (JXG.isFunction(f)) {
board.create('functiongraph',[JXG.Math.Numerics.D(f),
function(){
var c = new JXG.Coords(JXG.COORDS_BY_SCREEN,[0,0],board);
return c.usrCoords[1];
},
function(){
var c = new JXG.Coords(JXG.COORDS_BY_SCREEN,[board.canvasWidth,0],board);
return c.usrCoords[1];
}], {dash:2});
}
}