How do I target ES2018 in TypeScript?

Question

I am targeting ES2018 and do not care about ES3 or ES5. From my tsconfig.json: "target": "ES2018". tsc complains:

An async function or method in ES5/ES3 requires the 'Promise' constructor. Make sure you have a declaration for the 'Promise' constructor or include 'ES2015' in your --lib option.

I know I could add "lib": ["es2015"] to add libraries to the compilation but I don't need those libraries, I am targeting ES2018.

How do I target ES2018 in TypeScript?

Here is my tsconfig.json:

{
    "compilerOptions": {
            /* Basic Options */
            "target": "ES2018" /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017','ES2018' or 'ESNEXT'. */,
            "module": "commonjs" /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */,
            "lib": ["es2015"] /* Specify library files to be included in the compilation. */,
            // "allowJs": true,                       /* Allow javascript files to be compiled. */
            // "checkJs": true,                       /* Report errors in .js files. */
            // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
            // "declaration": true,                   /* Generates corresponding '.d.ts' file. */
            // "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
            // "sourceMap": true,                     /* Generates corresponding '.map' file. */
            // "outFile": "./",                       /* Concatenate and emit output to single file. */
            // "outDir": "./",                        /* Redirect output structure to the directory. */
            // "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
            // "composite": true,                     /* Enable project compilation */
            // "removeComments": true,                /* Do not emit comments to output. */
            // "noEmit": true,                        /* Do not emit outputs. */
            // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
            // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
            // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */

            /* Strict Type-Checking Options */
            "strict": true /* Enable all strict type-checking options. */,
            // "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
            // "strictNullChecks": true,              /* Enable strict null checks. */
            // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
            // "strictPropertyInitialization": true,  /* Enable strict checking of property initialization in classes. */
            // "noImplicitThis": true,                /* Raise error on 'this' expressions with an implied 'any' type. */
            // "alwaysStrict": true,                  /* Parse in strict mode and emit "use strict" for each source file. */

            /* Additional Checks */
            // "noUnusedLocals": true,                /* Report errors on unused locals. */
            // "noUnusedParameters": true,            /* Report errors on unused parameters. */
            // "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
            // "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */

            /* Module Resolution Options */
            // "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
            // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
            // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
            // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
            // "typeRoots": [],                       /* List of folders to include type definitions from. */
            // "types": [],                           /* Type declaration files to be included in compilation. */
            // "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
            "esModuleInterop": true /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
            // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */

            /* Source Map Options */
            // "sourceRoot": "",                      /* Specify the location where debugger should locate TypeScript files instead of source locations. */
            // "mapRoot": "",                         /* Specify the location where debugger should locate map files instead of generated locations. */
            // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
            // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */

            /* Experimental Options */
            // "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
            // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
    }
}

Pusillanimity

Could you post your entire tsconfig.json ? Also are you sure that the tsconfig.json that is getting picked up is the one with the ES2018 target ? – Disbranch

@TitianCernicova-Dragomir Sure, and no, I am not, since -p . doesn't work. – Pusillanimity

The "lib" parameter is meant to allow the definition files of certain constructs (like Promises) to be understood by the compiler. It does not add files to the actual build. It's fine to add es2015 (or es2018) there. You can also omit lib, in which case TS uses the sensible defaults based on the target, but that might not be working for ES2018. – Angelenaangeleno

What are the default libs for target ES2018? typescriptlang.org/docs/handbook/compiler-options.html specifies the defaults for targets ES5 and ES6 but not ES2018. – Airliah

Answer 1

Just add ES2018 to lib in tsconfig.json:

"lib": [
  "ES2018"
]

lib is different to target. target roughly means the JavaScript version of the generated output files. lib means the features you will use in TypeScript. For example, you can use new features in ES2018 ("lib": ["ES2018"]), but still target at ES6 ("target": "ES6"). Those new features will be translated to ES6 during compilation (this may be done via third party tools like babel, and some new features may not be translatable, but these are just implementation details).

Marsden