feat: Allow user to set browser preferences

README.md

@@ -40,6 +40,11 @@ npm install chrome-launcher
   // Do note, many flags are set by default: https://github.com/GoogleChrome/chrome-launcher/blob/master/src/flags.ts
   chromeFlags: Array<string>;
 
+  // (optional) Additional preferences to be set in Chrome, for example: {'download.default_directory': __dirname}
+  // See: https://chromium.googlesource.com/chromium/src/+/main/chrome/common/pref_names.cc
+  // Do note, if you set preferences when using your default profile it will overwrite these
+  prefs: {[key: string]: Object};
+
   // (optional) Close the Chrome process on `Ctrl-C`
   // Default: true
   handleSIGINT: boolean;

src/chrome-launcher.ts

@@ -26,9 +26,12 @@ type SupportedPlatforms = 'darwin'|'linux'|'win32'|'wsl';
 
 const instances = new Set<Launcher>();
 
+type JSONLike =|{[property: string]: JSONLike}|readonly JSONLike[]|string|number|boolean|null;
+
 export interface Options {
   startingUrl?: string;
   chromeFlags?: Array<string>;
+  prefs?: Record<string, JSONLike>;
   port?: number;
   handleSIGINT?: boolean;
   chromePath?: string;
@@ -105,6 +108,7 @@ class Launcher {
   private chromePath?: string;
   private ignoreDefaultFlags?: boolean;
   private chromeFlags: string[];
+  private prefs: Record<string, JSONLike>;
   private requestedPort?: number;
   private connectionPollInterval: number;
   private maxConnectionRetries: number;
@@ -127,6 +131,7 @@ class Launcher {
     // choose the first one (default)
     this.startingUrl = defaults(this.opts.startingUrl, 'about:blank');
     this.chromeFlags = defaults(this.opts.chromeFlags, []);
+    this.prefs = defaults(this.opts.prefs, {});
     this.requestedPort = defaults(this.opts.port, 0);
     this.chromePath = this.opts.chromePath;
     this.ignoreDefaultFlags = defaults(this.opts.ignoreDefaultFlags, false);
@@ -197,6 +202,8 @@ class Launcher {
     this.outFile = this.fs.openSync(`${this.userDataDir}/chrome-out.log`, 'a');
     this.errFile = this.fs.openSync(`${this.userDataDir}/chrome-err.log`, 'a');
 
+    this.setBrowserPrefs();
+
     // fix for Node4
     // you can't pass a fd to fs.writeFileSync
     this.pidFile = `${this.userDataDir}/chrome.pid`;
@@ -206,6 +213,28 @@ class Launcher {
     this.tmpDirandPidFileReady = true;
   }
 
+  private setBrowserPrefs() {
+    // don't set prefs if not defined
+    if (Object.keys(this.prefs).length === 0) {
+      return;
+    }
+
+    const preferenceFile = `${this.userDataDir}/Preferences`;
+    try {
+      if (this.fs.existsSync(preferenceFile)) {
+        // overwrite existing file
+        const file = this.fs.readFileSync(preferenceFile, 'utf-8');
+        const content = JSON.parse(file);
+        this.fs.writeFileSync(preferenceFile, JSON.stringify({...content, ...this.prefs}), 'utf-8');
+      } else {
+        // create new Preference file
+        this.fs.writeFileSync(preferenceFile, JSON.stringify({...this.prefs}), 'utf-8');
+      }
+    } catch (err) {
+      log.log('ChromeLauncher', `Failed to set browser prefs: ${err.message}`);
+    }
+  }
+
   async launch() {
     if (this.requestedPort !== 0) {
       this.port = this.requestedPort;
@@ -259,7 +288,9 @@ class Launcher {
           {detached: true, stdio: ['ignore', this.outFile, this.errFile], env: this.envVars});
       this.chrome = chrome;
 
-      this.fs.writeFileSync(this.pidFile, chrome.pid.toString());
+      if (chrome.pid) {
+        this.fs.writeFileSync(this.pidFile, chrome.pid.toString());
+      }
 
       log.verbose('ChromeLauncher', `Chrome running with pid ${chrome.pid} on port ${this.port}.`);
       return chrome.pid;
@@ -347,7 +378,9 @@ class Launcher {
             // if you don't explicitly set `stdio`
             execSync(`taskkill /pid ${this.chrome.pid} /T /F`, {stdio: 'pipe'});
           } else {
-            process.kill(-this.chrome.pid);
+            if (this.chrome.pid) {
+              process.kill(-this.chrome.pid);
+            }
           }
         } catch (err) {
           const message = `Chrome could not be killed ${err.message}`;

test/chrome-launcher-test.ts

@@ -64,6 +64,37 @@ describe('Launcher', () => {
     assert.strictEqual(fs.rmdir.callCount, 0);
   });
 
+  it('allows to overwrite browser prefs', async () => {
+    const existStub = stub().returns(true)
+    const readFileStub = stub().returns(JSON.stringify({ some: 'prefs' }))
+    const writeFileStub = stub()
+    const fs = {...fsMock, rmdir: spy(), readFileSync: readFileStub, writeFileSync: writeFileStub, existsSync: existStub };
+    const chromeInstance =
+        new Launcher({prefs: {'download.default_directory': '/some/dir'}}, {fs: fs as any});
+
+    chromeInstance.prepare();
+    assert.equal(
+      writeFileStub.getCall(0).args[1],
+      '{"some":"prefs","download.default_directory":"/some/dir"}'
+    )
+  });
+
+  it('allows to set browser prefs', async () => {
+    const existStub = stub().returns(false)
+    const readFileStub = stub().returns(Buffer.from(JSON.stringify({ some: 'prefs' })))
+    const writeFileStub = stub()
+    const fs = {...fsMock, rmdir: spy(), readFileSync: readFileStub, writeFileSync: writeFileStub, existsSync: existStub };
+    const chromeInstance =
+        new Launcher({prefs: {'download.default_directory': '/some/dir'}}, {fs: fs as any});
+
+    chromeInstance.prepare();
+    assert.equal(readFileStub.getCalls().length, 0)
+    assert.equal(
+      writeFileStub.getCall(0).args[1],
+      '{"download.default_directory":"/some/dir"}'
+    )
+  });
+
   it('cleans up the tmp dir after closing', async () => {
     const rmdirMock = stub().callsFake((_path, _options, done) => done());
     const fs = {...fsMock, rmdir: rmdirMock};