added check for [bins] argument in fft method of P5, along with unit Test( in es6 style)

src/fft.js

@@ -2,6 +2,7 @@
 
 define(function(require) {
   var p5sound = require('master');
+  const {safeBins} = require('helpers');
 
   /**
    *  <p>FFT (Fast Fourier Transform) is an analysis algorithm that
@@ -115,7 +116,7 @@ define(function(require) {
 
     // set default smoothing and bins
     this.smooth(smoothing);
-    this.bins = bins || 1024;
+    this.bins = safeBins(bins) || 1024;
 
     // default connections to p5sound fftMeter
     p5sound.fftMeter.connect(this.analyser);

src/helpers.js

@@ -322,7 +322,7 @@ define(function (require) {
   }
 
   function safeBufferSize(idealBufferSize) {
-    let bufferSize = idealBufferSize;
+    let bufferSize = idealBufferSize; 
 
     // if the AudioWorkletNode is actually a ScriptProcessorNode created via polyfill,
     // make sure that our chosen buffer size isn't smaller than the buffer size automatically
@@ -337,12 +337,27 @@ define(function (require) {
 
     return bufferSize;
   }
+ var safeBins =  p5.prototype.safeBins  = function(bins) {
+    let safeBins = 1024;
+    if(typeof(bins)==="string"){
+      console.log("the value of bins must be power of two and between 16 and 1024");
+      return safeBins
+    }
+    if(bins && bins>=16 && bins<=1024 && Math.log2(bins)%1===0 ) 
+    return bins;
+    else {
+      console.log("the value of bins must be power of two and between 16 and 1024");
+      return safeBins
+    }
+
+  }
 
   return {
     convertToWav: convertToWav,
     midiToFreq: midiToFreq,
     noteToFreq: noteToFreq,
-    safeBufferSize: safeBufferSize
+    safeBufferSize: safeBufferSize,
+    safeBins:safeBins
   };
 
 });

test/test.js

@@ -8,6 +8,7 @@ require.config({
 });
 
 var allTests = [
+  'tests/utils/test.helpers',
   'tests/p5.SoundFile',
   'tests/p5.Amplitude',
   'tests/p5.Oscillator',

test/tests/utils/test.helpers.js

@@ -0,0 +1,35 @@
+'use strict';
+
+define(['chai'],(chai)=>{
+    const safeBins = p5.prototype.safeBins;
+    let expect = chai.expect;
+
+    describe('safeBins', ()=>{
+        it('can handle negative input ',()=>{
+            let test =-Math.random()*2;
+            expect(safeBins(test)).to.equal(1024);
+        });
+        it('can handle value less than 16 ',()=>{
+            let test = 10;
+            expect(safeBins(test)).to.equal(1024);
+        });
+        it('can handle value greater than 1024',()=>{
+            let test = 1500;
+            expect(safeBins(test)).to.equal(1024);
+        });
+        it('can handle value other than power 2',()=>{
+            let test = 1500;
+            expect(safeBins(test)).to.equal(1024);
+        });
+        it('can handle value equal to 0',()=>{
+            let test = 0;
+            expect(safeBins(test)).to.equal(1024);
+        });
+        it('can handle strings',()=>{
+            let test = 'testString';    
+            expect(safeBins(test)).to.equal(1024);
+        });
+
+    });
+
+});