Improve error when relative path is passed to the directory option

Closes #143

index.d.ts

@@ -26,7 +26,9 @@ declare namespace electronDl {
 		readonly saveAs?: boolean;
 
 		/**
-		Directory to save the file in.
+		The directory to save the file in.
+
+		Must be an absolute path.
 
 		Default: [User's downloads directory](https://electronjs.org/docs/api/app/#appgetpathname)
 		*/

index.js

@@ -67,7 +67,12 @@ function registerListener(session, options, callback = () => {}) {
 
 		const window_ = majorElectronVersion() >= 12 ? BrowserWindow.fromWebContents(webContents) : getWindowFromWebContents(webContents);
 
+		if (options.directory && !path.isAbsolute(options.directory)) {
+			throw new Error('The `directory` option must be an absolute path');
+		}
+
 		const directory = options.directory || app.getPath('downloads');
+
 		let filePath;
 		if (options.filename) {
 			filePath = path.join(directory, options.filename);

index.test-d.ts

@@ -1,5 +1,3 @@
-/// <reference lib="dom"/>
-/// <reference types="node"/>
 import {expectType} from 'tsd';
 import {BrowserWindow, DownloadItem} from 'electron';
 import electronDl = require('.');

readme.md

@@ -92,7 +92,9 @@ Note: Only use this option when strictly necessary. Downloading directly without
 Type: `string`\
 Default: [User's downloads directory](https://electronjs.org/docs/api/app/#appgetpathname)
 
-Directory to save the file in.
+The directory to save the file in.
+
+Must be an absolute path.
 
 #### filename