Enhance error message

Author: jeromewu

src/browser/getCreateFFmpegCore.js

@@ -1,6 +1,9 @@
 /* eslint-disable no-undef */
 const resolveURL = require('resolve-url');
 const { log } = require('../utils/log');
+const {
+  CREATE_FFMPEG_CORE_IS_NOT_DEFINED,
+} = require('../utils/errors');
 
 /*
  * Fetch data from remote URL and convert to blob URL
@@ -38,6 +41,9 @@ module.exports = async ({ corePath: _corePath }) => {
       const script = document.createElement('script');
       const eventHandler = () => {
         script.removeEventListener('load', eventHandler);
+        if (typeof createFFmpegCore === 'undefined') {
+          throw Error(CREATE_FFMPEG_CORE_IS_NOT_DEFINED(coreRemotePath));
+        }
         log('info', 'ffmpeg-core.js script loaded');
         resolve({
           createFFmpegCore,

src/utils/errors.js

@@ -0,0 +1,11 @@
+const CREATE_FFMPEG_CORE_IS_NOT_DEFINED = (corePath) => (`
+createFFmpegCore is not defined. ffmpeg.wasm is unable to find createFFmpegCore after loading ffmpeg-core.js from ${corePath}. Use another URL when calling createFFmpeg():
+
+const ffmpeg = createFFmpeg({
+  corePath: 'http://localhost:3000/ffmpeg-core.js',
+});
+`);
+
+module.exports = {
+  CREATE_FFMPEG_CORE_IS_NOT_DEFINED,
+};