The Web Audio API
Notes
FIll in the coefficients and frequencies on the left to create an arbitrary Fourier equation with 6 terms. Then select Equation as the Curve Type and click Plot Equation.
Other curve types are also available for convenience. In this case you only need specify the Number of Terms and the relevant coefficients and frequencies will be automatically computed.
The special cases are interesting. The square wave and F(x) are well known. The Harmonics wave starts with a frequency of 1Hz and doubles the frequency for each term in the equation, thus giving all the harmonics of 1Hz. The Linear Frequency simple takes frequencies of 1Hz, 2, 3, 4, ... up to however many terms you want to include. In both cases the coefficients are all 1.0. Note that the Linear wave actually tends to zero (except for a singularity at each end).