Question

I am trying to make a graph of a simple function y=k*x+b.
A user enters a function into the input field, for example:

1/3*x+3

and when he/she clicks the submit button, a JavaScript function is supposed to take this input value as an actual calculation sequence and assign a variable to it (I only need to get certain y values here, so the x variable has its limits):

for (x=1;x<=40;x++)
{
    result = window.document.menu.inputFunction.value;
}

The above code doesn’t work. No wonder why – I am just a beginner at this. However, is this really harder than it looks, or am I missing out something? I considered trying regular expressions for this at one point, but my head hurts by even thinking about using them.

Any ideas?

Answer 1

You could eval it:

result = eval(window.document.menu.inputFunction.value);

There are obviously some limitations to this approach:

• The user must enter a valid javascript expression
• The user must use x as variable name because that’s what you are using in the loop
• The code is vulnerable because the user can enter and execute any javascript expression he likes

For a more robust solution you might consider using a javascript mathematical expression evaluator.