Use default arguments

packages/pegjs/lib/compiler/index.js

@@ -49,9 +49,7 @@ const compiler = {
     // if the AST contains a semantic error. Note that not all errors are detected
     // during the generation and some may protrude to the generated parser and
     // cause its malfunction.
-    compile( ast, session, options ) {
-
-        options = typeof options !== "undefined" ? options : {};
+    compile( ast, session, options = {} ) {
 
         options = util.processOptions( options, {
             allowedStartRules: [ ast.rules[ 0 ].name ],

packages/pegjs/lib/compiler/session.js

@@ -19,9 +19,7 @@ function fatal( message, location ) {
 
 class Session {
 
-    constructor( config ) {
-
-        config = typeof config !== "undefined" ? config : {};
+    constructor( config = {} ) {
 
         this.opcodes = config.opcodes || opcodes;
         this.parser = config.parser || parser;

packages/pegjs/lib/peg.js

@@ -25,9 +25,7 @@ const peg = {
     // |peg.GrammarError| if it contains a semantic error. Note that not all
     // errors are detected during the generation and some may protrude to the
     // generated parser and cause its malfunction.
-    generate( grammar, options ) {
-
-        options = typeof options !== "undefined" ? options : {};
+    generate( grammar, options = {} ) {
 
         const session = new compiler.Session( {
             passes: util.convertPasses( compiler.passes )