[wasm] Tidy up wasm-module-builder.js

Fix some JS smells as suggested in
https://github.com/WebAssembly/spec/issues/897.

R=ahaas@chromium.org

Bug: v8:8238
Change-Id: Idc4f738da849f28477563df628dcae2805b1b47e
Reviewed-on: https://chromium-review.googlesource.com/c/1301476Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57029}

test/mjsunit/wasm/wasm-module-builder.js

@@ -84,10 +84,11 @@ class WasmFunctionBuilder {
     this.name = name;
     this.type_index = type_index;
     this.body = [];
+    this.locals = [];
+    this.local_names = [];
   }
 
   numLocalNames() {
-    if (this.local_names === undefined) return 0;
     let num_local_names = 0;
     for (let loc_name of this.local_names) {
       if (loc_name !== undefined) ++num_local_names;
@@ -123,7 +124,7 @@ class WasmFunctionBuilder {
 
   getNumLocals() {
     let total_locals = 0;
-    for (let l of this.locals || []) {
+    for (let l of this.locals) {
       for (let type of ["i32", "i64", "f32", "f64", "s128"]) {
         total_locals += l[type + "_count"] || 0;
       }
@@ -133,10 +134,8 @@ class WasmFunctionBuilder {
 
   addLocals(locals, names) {
     const old_num_locals = this.getNumLocals();
-    if (!this.locals) this.locals = []
     this.locals.push(locals);
     if (names) {
-      if (!this.local_names) this.local_names = [];
       const missing_names = old_num_locals - this.local_names.length;
       this.local_names.push(...new Array(missing_names), ...names);
     }
@@ -242,7 +241,7 @@ class WasmModuleBuilder {
     return func;
   }
 
-  addImport(module = "", name, type) {
+  addImport(module, name, type) {
     if (this.functions.length != 0) {
       throw new Error('Imported functions must be declared before local ones');
     }
@@ -252,7 +251,7 @@ class WasmModuleBuilder {
     return this.num_imported_funcs++;
   }
 
-  addImportedGlobal(module = "", name, type, mutable = false) {
+  addImportedGlobal(module, name, type, mutable = false) {
     if (this.globals.length != 0) {
       throw new Error('Imported globals must be declared before local ones');
     }
@@ -262,20 +261,20 @@ class WasmModuleBuilder {
     return this.num_imported_globals++;
   }
 
-  addImportedMemory(module = "", name, initial = 0, maximum, shared) {
+  addImportedMemory(module, name, initial = 0, maximum, shared) {
     let o = {module: module, name: name, kind: kExternalMemory,
              initial: initial, maximum: maximum, shared: shared};
     this.imports.push(o);
     return this;
   }
 
-  addImportedTable(module = "", name, initial, maximum) {
+  addImportedTable(module, name, initial, maximum) {
     let o = {module: module, name: name, kind: kExternalTable, initial: initial,
              maximum: maximum};
     this.imports.push(o);
   }
 
-  addImportedException(module = "", name, type) {
+  addImportedException(module, name, type) {
     if (this.exceptions.length != 0) {
       throw new Error('Imported exceptions must be declared before local ones');
     }