Language Support

TypeScript

Cocos Creator supports TypeScript 4.1.0. The following restrictions are based on TypeScript 4.1.0:

• tsconfig.json will not be read. The following options are implied for each project:

  {
    "compilerOptions": {
        "target": "ES2015",
        "module": "ES2015",
        "isolatedModules": true,
        "experimentalDecorators": true,
        "moduleResolution": /* Cocos Creator's specific module resolution algorithm */,
        "forceConsistentCasingInFileNames": true,
    }，
  }

  The implicit isolatedModules option means that:

  • const enums is not supported.

  • Use export type when re-exporting TypeScript types and interfaces. For example, use export type { Foo } from '. /foo'; instead of export { Foo } from '. /foo';.

• export = and import = are not supported.

• Variables derived from namespace must be declared as const, not var or let.

• Different declarations in the same namespace do not share scope and require explicit use of qualifiers.

• Type errors during compilation will be ignored.

tsconfig.json is not read at compile time, meaning that the compile option for tsconfig.json does not affect compilation.

Developers can still use tsconfig.json in their projects to work with the IDE to implement features such as type checking. In order to make the IDE’s TypeScript checking compatible with the Creator’s behavior, developers need to pay some extra attention to tsconfig.

JavaScript

Language Features

The JavaScript language specification supported by the Creator is ES6.

In addition, the following language features or proposals, updated to the ES6 specification, are still supported.

• Public class fields
• Promise
• Optional chaining operator ?.
• Nullish coalescing operator ??
• Logical assignment operators
  • Logical nullish assignment operator ??=
  • Logical AND assignment operator &&=
  • Logical OR assignment operator ||=
• Global object globalThis

The following language features are also supported, but require the relevant compilation options to be turned on:

• async functions

In particular, Creator currently supports Legacy decorator proposals, see babel-plugin-proposal-decorators for their usage and meaning. Since this proposal is still in phase 2, all decorator-related functional interfaces exposed by the engine are under the _decorator namespace starting with an underscore.

Compilation Options

Creator opens some compilation options that will be applied to the entire project.

Runtime Environment

From the user’s perspective, Creator does not bind any JavaScript implementation, so it is recommended that developers write scripts strictly according to the JavaScript specification for better cross-platform support.

For example, when wishing to use global objects, the standard feature globalThis should be used:

globalThis.blahBlah // 'globalThis' must exist in any environment

instead of window, global, self or this:

typeof window // May be 'undefined'
typeof global // May be 'undefined' in the browser environment

Again, Creator does not provide a module system for CommonJS, so the following code snippet would pose a problem:

const blah = require('./blah-blah'); // Error, require is undefined
module.exports = blah; // Error, module is undefined

Instead, the standard module syntax should be used:

import blah from './blah-blah';
export default blah;

Related Tutorials

• JavaScript Standard Reference Tutorial [cn]
• JavaScript Garden
• JavaScript Memory Detailing & Analysis Guide [cn]