WebGL screenshot

I'm using Unity 5.6.4 and I've got a game where you've got to find a bunch of stuff and when you find them all you go to a scene where there's confetti raining down and it says "you took xx:xx:xx" I want a button at the bottom where you click and it save a screenshot of the time taken. the game will be on a site and as an .exe. I've got the screenshot for the .exe version done and working it the downloading it from webGL that isn't working. I know I need a .jslib to have the download function and then call that from the unity script.

In Assets/Plugins I've got download.jslib

Code (JavaScript):

1. mergeInto(LibraryManager.library, {
2.   Download: function (data, filename, type) {
3.     var file = new Blob([data], {type: type});
4.     if (window.navigator.msSaveOrOpenBlob) // IE10+
5.         window.navigator.msSaveOrOpenBlob(file, filename);
6.     else { // Others
7.         var a = document.createElement("a"),
8.                 url = URL.createObjectURL(file);
9.         a.href = url;
10.         a.download = filename;
11.         document.body.appendChild(a);
12.         a.click();
13.         setTimeout(function() {
14.             document.body.removeChild(a);
15.             window.URL.revokeObjectURL(url);
16.         }, 0);
17.     }
18.   }
19.  
20. });

This is called in the unity file save_Screenshot.cs

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using System.Runtime.InteropServices;
4. using UnityEngine;
5.  
6. public class Save_Screenshot : MonoBehaviour {
7.  
8.     [DllImport("__Internal")]
9.     private static extern void Download(byte[] data, string filename, string type);
10.  
11.     private static Save_Screenshot instance;
12.  
13.     private Camera myCamera;
14.     private bool takeScreenshot = false;
15.  
16.     private void Awake () {
17.         instance = this;
18.         myCamera = gameObject.GetComponent<Camera> ();
19.     }
20.  
21.     private void TakeScreenshot(int width, int height){
22.         myCamera.targetTexture = RenderTexture.GetTemporary (width, height, 16);
23.         takeScreenshot = true;
24.     }
25.  
26.     IEnumerator OnPostRender() {
27.         if (takeScreenshot) {
28.             yield return new WaitForEndOfFrame ();
29.             takeScreenshot = false;
30.             RenderTexture renderTexture = myCamera.targetTexture;
31.  
32.             Texture2D renderResult = new Texture2D (renderTexture.width, renderTexture.height, TextureFormat.ARGB32, false);
33.             Rect rect = new Rect (0, 0, renderTexture.width, renderTexture.height);
34.             renderResult.ReadPixels (rect, 0, 0);
35.  
36.             byte[] byteArray = renderResult.EncodeToPNG ();
37.             Download (byteArray, "Time Taken.png", "image/png");
38.  
39.             RenderTexture.ReleaseTemporary (renderTexture);
40.             myCamera.targetTexture = null;
41.         }
42.     }
43.  
44.     public static void staticScreenshot(int width, int height){
45.         instance.TakeScreenshot (width, height);
46.     }
47. }

When i run this in editor to test it I get an error

EntryPointNotFoundException: Download

Save_Screenshot+<OnPostRender>c__Iterator0.MoveNext () (at Assets/Scripts/Save_Screenshot.cs:38)

UnityEngine.SetupCoroutine.InvokeMoveNext (IEnumerator enumerator, IntPtr returnValueAddress) (at C:/buildslave/unity/build/Runtime/Export/Coroutines.cs:17)

Thinking this may be because I'm trying to do it in editor not on a browser i tried to build it but I got a error saying its failed its sanity check

LSupport\\BuildTools\\emscripten.config_sanity'

stderr:WARNING:root:did not see a source tree above or next to the LLVM root directory (guessing based on directory of C:\Program Files\Unity\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten_FastComp_Win\llc), could not verify version numbers match

INFO:root:(Emscripten: Running sanity checks)

WARNING:root:java does not seem to exist, required for closure compiler, which is optional (define JAVA in C:\Program Files\Unity\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\emscripten.config if you want it)

WARNING:root:closure compiler will not be available

WARNING:root:--separate-asm works best when compiling to HTML. otherwise, you must yourself load the '.asm.js' file that is emitted separately, and must do so before loading the main '.js` file

error: failure to execute js library "L:\unity\Test\Assets\Plugins\test.jslib": SyntaxError: Unexpected token ILLEGAL,,SyntaxError: Unexpected token ILLEGAL    at Object.LibraryManager.load (eval at globalEval (C:\Program Files\Unity\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten\src\compiler.js:105:8), <anonymous>:173:14)    at JSify (eval at globalEval (C:\Program Files\Unity\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten\src\compiler.js:105:8), <anonymous>:59:20)    at L:\unity\Test\Assets\Plugins\test.jslib (C:\Program Files\Unity\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten\src\compiler.js:208:3)    at Module._compile (module.js:460:26)    at Object.Module._extensions..js (module.js:478:10)    at Module.load (module.js:355:32)    at Function.Module._load (module.js:310:12)    at Function.Module.runMain (module.js:501:10)    at startup (node.js:129:16)    at node.js:814:3preprocessed source (you can run a js engine on this to get a clearer error message sometimes):=============��m

UnityEditor.HostView:OnGUI()

And another error

L/Extensions/Unity.WebGL.extensions/BuildPostprocessor.cs:437)

UnityEditor.WebGL.WebGlBuildPostprocessor.PostProcess (BuildPostProcessArgs args) (at /Users/builduser/buildslave/unity/build/PlatformDependent/WebGL/Extensions/Unity.WebGL.extensions/BuildPostprocessor.cs:877)

UnityEditor.PostprocessBuildPlayer.Postprocess (BuildTargetGroup targetGroup, BuildTarget target, System.String installPath, System.String companyName, System.String productName, Int32 width, Int32 height, System.String downloadWebplayerUrl, System.String manualDownloadWebplayerUrl, BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry, UnityEditor.BuildReporting.BuildReport report) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:186)

UnityEditor.HostView:OnGUI()

Any idea what I'm doing wrong?