Browser: Add fetch for urls

browser.js

@@ -5,7 +5,7 @@ class PDFMerger {
     this._resetDoc()
   }
 
-  add (inputFile, pages) {
+  async add (inputFile, pages) {
     if (typeof pages === 'undefined' || pages === null) {
       return this._addEntireDocument(inputFile, pages)
     } else if (Array.isArray(pages)) {
@@ -39,19 +39,29 @@ class PDFMerger {
   }
 
   async _getInputFile (inputFile) {
-    return new Promise((resolve) => {
-      if (inputFile instanceof Buffer) {
-        resolve(inputFile)
-      } else {
-        const fileReader = new window.FileReader()
-
-        fileReader.onload = function (evt) {
-          resolve(fileReader.result)
-        }
+    if (inputFile instanceof Buffer || inputFile instanceof ArrayBuffer) {
+      return inputFile
+    }
+    if (typeof inputFile === 'string' || inputFile instanceof String) {
+      const res = await window.fetch(inputFile)
+      const ab = await res.arrayBuffer()
+      return ab
+    }
+    if (inputFile instanceof window.File) {
+      const fileReader = new window.FileReader()
 
-        fileReader.readAsArrayBuffer(inputFile)
+      fileReader.onload = function (evt) {
+        return fileReader.result
       }
-    })
+
+      fileReader.readAsArrayBuffer(inputFile)
+    }
+
+    if (inputFile instanceof window.Blob) {
+      return await inputFile.arrayBuffer()
+    }
+
+    throw new Error('pdf must be represented as an ArrayBuffer, Blob, Buffer, File, or URL')
   }
 
   async _addEntireDocument (inputFile) {

package.json

@@ -28,6 +28,8 @@
   "devDependencies": {
     "fs-extra": "^10.0.0",
     "jest": "^27.0.6",
+    "jsdom": "^16.7.0",
+    "node-fetch": "^2.6.1",
     "pdf-diff": "^0.1.1",
     "standard": "^16.0.3"
   }