Add newInstance option for macOS (#253)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.d.ts

@@ -22,6 +22,17 @@ declare namespace open {
 		*/
 		readonly background?: boolean;
 
+		/**
+		__macOS only__
+
+		Open a new instance of the app even it's already running.
+
+		A new instance is always opened on other platforms.
+
+		@default false
+		*/
+		readonly newInstance?: boolean;
+
 		/**
 		Specify the `name` of the app to open the `target` with and optionally, app `arguments`. `app` can be an array of apps to try to open and `name` can be an array of app names to try. If each app fails, the last error will be thrown.
 

index.js

@@ -77,6 +77,7 @@ const open = async (target, options) => {
 	options = {
 		wait: false,
 		background: false,
+		newInstance: false,
 		allowNonzeroExitCode: false,
 		...options
 	};
@@ -115,6 +116,10 @@ const open = async (target, options) => {
 			cliArguments.push('--background');
 		}
 
+		if (options.newInstance) {
+			cliArguments.push('--new');
+		}
+
 		if (app) {
 			cliArguments.push('-a', app);
 		}

readme.md

@@ -80,6 +80,15 @@ Default: `false`
 
 Do not bring the app to the foreground.
 
+##### newInstance <sup>(macOS only)</sup>
+
+Type: `boolean`\
+Default: `false`
+
+Open a new instance of the app even it's already running.
+
+A new instance is always opened on other platforms.
+
 ##### app
 
 Type: `{name: string | string[], arguments?: string[]} | Array<{name: string | string[], arguments: string[]}>`