Using the `fft` library from `npm`.

index.js

var FFT = require('fft');

FFT_SIZE = 8;

var fft = new FFT.complex(FFT_SIZE, false);
var ifft = new FFT.complex(FFT_SIZE, true);

var inBuffer = new Float32Array([0,.5,1,.5,0,-.5,-1,-.5]);
var outBuffer = new Float32Array(2 * FFT_SIZE);
var outBuffer2 = new Float32Array(2 * FFT_SIZE);

console.log('inBuffer...');
console.log(Array.prototype.slice.call(inBuffer));

fft.simple(outBuffer, inBuffer, 'real');

console.log('outBuffer...');
console.log(Array.prototype.slice.call(outBuffer));

ifft.simple(outBuffer2, outBuffer);

console.log('outBuffer2...');
console.log(Array.prototype.slice.call(outBuffer2));

var realOut = [];
for (var i=0; i<FFT_SIZE; i++) {
    realOut[i] = outBuffer2[2*i] / FFT_SIZE;
}

console.log('realOut...');
console.log(realOut);