Writing a JavaScript Function

Below you find the JavaScript code for our function `check()` that checks whether the entered equation is correct. Our GeoGebra construction contains several objects to help us with checking the user input in JavaScript. The construction includes the function `f(x)`, its derivative `h(x)` and a function `g(x) = 0` that the user will be able to change using the input field on the web page. Furthermore, we have added a function `diff(x) = Polynomial[ h(x) - g(x)]` that shows the difference of the derivative `h(x)` and the user's answer `g(x)` as a polynomial in standard form. Thus, we only need to check if `diff(x) = 0`. Both `h(x)` and `diff(x)` are hidden objects in the GeoGebra construction.

```1. <script>
1. function check() {
2.
3.    var applet = document.ggbApplet;
4.    applet.evalCommand("g(x) = " + document.inputform.textfield.value);
4.    var diffString = applet.getValueString("diff");
5.    if (diffString == "diff(x) = 0") {
The first and last lines are the beginning and end of the JavaScript block in our HTML page which need to surround our declaration of the `check()` function. In line 4 we take the user's input to set the hidden function `g(x)`. Then we get the equation of `diff(x)` and check whether it's 0, i.e. if the the user entered the correct solution (line 6). In case of a wrong answer we show the graph of the solution `h(x)` to provide some feedback about the mistake (lines 10-12). If the answer was correct, we make sure that our hint, the graph of the derivative `h(x)`, is hidden again (lines 7-8).