Compact Fast Fourier transform function in JavaScript based on the Cooley–Tukey algorithm with a demo page that illustrates the use of window functions and a simple spectrogram.

• Clone the repository
• Open the file index.html with any web browser

This demo also illustrates the use of window functions and a simple spectrogram.

https://ciiec.buap.mx/FFT.js/

Assuming x is the time domain array of size N with the sampled data, where N is a power of 2, then

 fft = FFT(x);

 X_real = new Array(my_x.length / 2).fill(0);

 X_imag = new Array(my_x.length / 2).fill(0);

 X_abs = new Array(my_x.length / 2).fill(0);

 for (var i = 0; i < N / 2; i += 1) {

     X_real[i] = fft[i].re;
  
     X_imag[i] = fft[i].im;
  
     X_abs[i] = Math.sqrt(fft[i].re * fft[i].re + fft[i].im * fft[i].im);

 }

where

fft is FFT{x} and X_real, X_imag and X_abs are the frequency domain arrays containing the real, imaginary and absolute values, respectively. The size of fft is N and the size of the other arrays is N/2.

• The FFT function was adapted from https://rosettacode.org/wiki/Fast_Fourier_transform#JavaScript

MIT