TSCC

TSCC is a collection of tools to seamlessly bundle and minify Typescript project using Closure Compiler.

Migrate

It is easy to migrate an existing Typescript project to TSCC. To get a sense of what it is like, check out todomvc apps forked from the original tastejs/todomvc and modified to use TSCC.

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Features

• Automatically configures settings for tsickle and closure compiler, and wires up tsickle js outputs and sourcemaps to closure compiler, sorted in accordence with dependency information, as required by closure compiler.
• Provides an alternative rollup build using rollup-plugin-tscc plugin, emulating the chunking behaviour of closure compiler to get the same set of output files as what closure compiler would produce.
• External module support: looks up required nodejs modules and wires them so that externs are generated, and transforms any code that uses externally imported variables. Think of it as an analogue of "external" option of webpack or "globals" option of rollup for closure compiler.

Background

Closure is a wonderful system of tools. The closure compiler is the best javascript minifier and bundler, but it is known to be very difficult to use. Documentations are scarce, and integration with external tools is not well-established.

Tsickle is another wonderful tool. It has finally made it ergonomic to write codes that can naturally be consumed by closure compiler — it transforms .ts files to well-annotated .js files, which would otherwise not even be consumed by the compiler and automatically generates externs file from declaration files. However, as in closure compiler, one has to be careful with setting it up, otherwise strange bugs can occur which are not actively worked on as of now. Also, it only performs transpilation — there is no tool to feed transpiled files to closure compiler, which is another painful part.

TSCC aims to encapsulate these tools in a minimal, ergonomic API, and provides a faster and easier alternative bundling method using Rollup via a companion rollup-plugin-tscc plugin, which is great for rapid development. TSCC can be used as a drop-in replacement for rollup in existing projects using rollup, after moving chunk information in rollup.config.js to tscc.spec.json. TSCC spec file is a single source of truth for all of your module bundling information.

Getting started

Suppose that we have a project with the following directory structure.

my_project
├───tsconfig.json
├───rollup.config.js
└───src
    ├───Components
    │   ...
    └───app.ts

1. Install tscc cli:

   yarn global add @tscc/tscc
   

2. Create a spec file tscc.spec.json next to tsconfig.json.

   {
       "modules": {
           "out": "src/app.ts" // entry file path
       }
   }

3. Execute at the project root:

   tscc
   

In order to setup an alternative rollup build,

1. In your project's directory, install @tscc/rollup-plugin-tscc by executing:

   yarn add -D @tscc/rollup-plugin-tscc
   

2. Import rollup-plugin-tscc plugin in rollup config file.

   // rollup.config.js
   import tscc from '@tscc/rollup-plugin-tscc';
   export default {
       output: {
           ...,
           dir: '.'
       },
       plugins: [
           tscc(),
           typescript()
       ]
   }

3. Execute rollup at the project root.

Usage

Command line

@tscc/tscc package provides a single command line interface tscc.

tscc [--help] [--clean] [--spec <spec_file_path>] [-- <typescript_flags> [-- <closure_compiler_flags>]]

It will compile & bundle typescript sourced based on module spec described in spec_file. Alternatively, one can provide the spec file's key-value pairs via command line arguments, see below. Note that one have to provide a spec file or at least a value for a 'module' - if both are omitted, it will assume that the spec file's path is implicitly set as the current working directory.

Arguments passed after the first --, if exists, will be passed to the typescript compiler as one would pass to tsc, and arguments after the second -- will be passed to the closure compiler. e.g. tscc --spec src -- --target ES5 -- --assume_function_wrapper. Note that tsc assumes that the project root (--project) is the current working directory when it is omitted, but tscc assumes that it is the containing directory of the spec file.

JS API

Simply provide contents of spec file as an argument:

import tscc from 'tscc';

tscc({
    modules: {
        bundle: 'entry.ts'
    },
    prefix: 'dist/'
    // ...
}).then(() => console.log('Done'));

The default export tscc function accepts up to 3 arguments.

tscc(
    json_content_of_spec_file_or_path_to_spec_file,
    path_to_search_for_tsconfig?:string,
    typescript_compiler_option_override?
):Promise<void>

The first argument is either a string representing the path of the spec file or a JSON content of the spec file. The JSON object can additionally have specFile property, whose value is a path to a spec file. TSCC will lookup tscc spec file at that path and merge its contents.

tscc({
    /* Contents of spec JSON */
    specFile: "path_to_spec_file.json"
})
// To load spec file from the path and override it.

The second argument should be self-explanatory; the third argument is what would you put in tsconfig.json's "compilerOption" key, it will override those provided with the second argument.

Usage with rollup

@tscc/rollup-plugin-tscc package provides a rollup plugin which will provide chunking information in your spec file to rollup.

Install rollup-plugin-tscc by executing yarn add -D @tscc/rollup-plugin-tscc.

// rollup.config.js
const tscc = require('@tscc/rollup-plugin-tscc');
module.exports = {
    output: {
        dir: '.' // output.dir option will be provided by the plugin, but
                 // rollup currently requires something to be present in order to
                 // work properly.
    },
    // ...
    plugins: [
        tscc({
            /* Contents of spec JSON */
            // or,
            specFile: "path_to_spec_file.json"
        })
    ]
};

Then it will provide the information in your spec file to rollup, and post-process code-splitting chunks produced by rollup to match the behavior of Closure Compiler, so that you can use rollup build interchangeably with tscc build. The plugin will control the input, output.dir, output.entryFileNames, output.chunkFileNames option. Note that it does not transpile TS to JS, one has to provide another plugin manually, such as rollup-plugin-typescript2.

Tscc spec files

Tscc spec file is a single source of truth of your bundling information. It describes each of output bundle's entry file and dependencies among them. It also describes which modules imported in your source shall be treated as an external module and aliased with which global variable.

{
    modules, /* required */
    external,
    prefix,
    chunkFormat,
    compilerFlags,
    jsFiles,
    debug
}

modules

    "modules": {
        "index": "index.ts",
        "dependent_a": {
            "entry": "dependent_a_entry_file.ts",
            "dependencies": [ "index" ],
            "extraSources": [ "css_renaming_map.js" ]
        }
    }

modules option is a key-value pair of module name and module's specification. If a specification only consists of a entry file name, it can simply be a string representing the entry file's path, which is sufficient for most of build situation where no code splitting is applied. In general, module's specification consists of entry, dependencies, and extraSources. dependencies is an array of module names that this module depends on. It can be omitted if empty. Module names specified here will be provided to closure compiler via --chunk flags, so check out a more detailed description of it in Closure Compiler repo. extraSources is an array of file names, which are not included in the Typescript project or not reacheable from a specified entry file via imports, but still needed to be provided to the closure compiler, such as css renaming maps generated by Closure Stylesheets. It can be omitted if empty. A module's name is an identifier to be used as a output chunk's name. To control the output directory, use prefix option.

CLI equivalent is --module <module_name>:<entry_file>:<comma_separated_dependencies>:<comma_separated_extra_sources>.

external

{
    "external": {
        "react": "React",
        "react-dom": "ReactDOM",
    }
}

It is mostly identical to the output.global option of rollup. It is a key-value pair, where key is a module name whose content will not be included in the bundle output, and value is a name of a global variable to which an module.exports of the module will be aliased.

If a module name is a relative path, the file it resolves to will be treated as an external module. This is similar to rollup's case, but is different in that only relative path can be used and absolute paths can't. Such paths are resolved in the same convention how other relative paths in the spec file are resolved, see prefix option description.

CLI equivalent is --external <module_name>:<global_variable_name>.

prefix

    "prefix": "dist/"
    // or,
    "prefix": { "rollup": "dev/", "cc": "dist/" }

It is a name that will be prepended to the output chunk's name. It is prepended as is, which means that if no trailing path separator was provided, it will modify the output file's name. If it is a relative path starting from the current directory ("."), it will be resolved relative to the spec file's location. Otherwise, any relative path will be resolved relative to the current working directory, and absolute paths are used as is.

CLI equivalent is --prefix dist/ (or --prefix.rollup dev/ --prefix.cc dist/).

chunkFormat

    "chunkFormat": "global" /* default */ | "module"

It is a value of "global" or "module" designating the output chunks' format. In case of "global", which is the default behavior if this key isn't specified, output chunks will be plain Javascript that is suitable for <script src=""> HTML tag, and cross-chunk references will be done by exposing them to the global scope. In case of "module", output chunks will be Javascript modules which has to be included via <script type="module" src=""> tags, and cross-chunk references will be done by import and export statements. Currently, when "module" option is used, external option cannot be used.

compilerFlags

    "compilerFlags": {
        "assume_function_wrapper": true,
        "rewrite_polyfills": true,
        "language_out": "ECMASCRIPT_2019",
        "variable_renaming_report": "out/report.map"
    }

It is a key-value pair of flags to be passed to the closure compiler. Keys are literally closure compiler options minus the leading --. flags which accepts multiple values can be represented as an array of values. TSCC sets default values for many flags, in particular, the compilation works even without the compilerOptions key in the spec. Any values provided here will override default flags. TSCC will treat these values as opaque data.

jsFiles

    "jsFiles": [
        "./glob/*/for/js/files.js"
    ]

It is a string or an array of string, containing glob expressions of JS files to be provided to closure compiler. In order to import closure-style JS to TS file, use import "goog:moduleName" in TS, and provide the JS file declaring goog.module('moduleName') via this flag. A difference with extraSources in module spec is that these files will be included in dependency graph just like other TS files, but extraSources will be included in the compilation even if they are not reachable from entry files.

debug

    "debug": {
        "persistArtifacts": true,
        "ignoreWarningsPath": ["/node_modules/", "/vendor/"]
    }

It is a key-value pair of debugging options.

• persistArtifacts: writes intermediate tsickle output to a directory .tscc_temp.
• ignoreWarningsPath: Paths to ignore warnings produced by tsickle. It uses a simple substring search. This value defaults to ["/node_modules/"].

Importing external libraries from NPM

Best practice is to provide them as a separate script tag instead of bundling it together, as such libraries do not in general safe to be compiled by Closure Compiler. Declare them as external modules in the spec file, and import them like you would usually do. Then you can benefit from IDE's type checking functionality while tscc can lookup their type definitions and include them as closure compiler's externs.

Detailed description of external modules handling

1. Users write import React from 'react', so that users' IDE can find necessary typings.
2. TSCC configures tsickle to process type declaration files of module 'react' that Typescript located for us -- usually in node_modules directory.
3. TSCC creates a hypothetical "gluing modules" for each of external modules that looks like

   goog.module('react')
   /** Generated by TSCC */
   exports = React

4. To inform Closure about such a user-provided global variable name, TSCC generates additional externs for such a global variable, like

   /**
    * @const
    * @type {some$file$name$mangled$by$tsickle}
    */
   var React = {};

   tsickle writes module-scoped externs to certain mangled namespace like this, so by declaring a global variable to be a type of that namespace, this provides type information of the external module to Closure Compiler.

How compilation source files are determined

In order to generate externs for external modules, TSCC has to provide declaration files to tsickle. Which files are provided? Typescript compiler's default behavior is hidden in most of cases, because .d.ts files does not anyway affect the compilation output. However, .d.ts files are used to generate externs in TSCC, so sometimes you may need to know this for troubleshooting.

The Typescript compiler's default behavior is to include every type declarations in ./node_modules/@types/, ../node_modules/@types/, ../../node_modules/@types/, ..., and if you specify "types": ["a", "b", ...] in compiler options, it instead only includes files in (../)node_modules/@types/a/ -- See official documentation on types and typeRoots.

In comparison, TSCC will only include a file when it is reachable from root files via transitive imports, triple-slash reference directives ///<reference path="..."/> and ///<reference types="..."/>. Root files will be the following:

• module entry points designated in the spec file,
• external module's base type declaration files,
• modules included in tsconfig.json types key.

Importing typescript sources in node_modules

In order for typescript sources in node_modules directory to be compiled, you need to explicitly include those files in your tsconfig.json. This is a rule imposed by the typescript compiler; it has some special handling for files in node_modules directory, it won't transpile such files unlike usual transitive dependencies (that is, files not explicitly included in tsconfig.json via "files" or "include" keys, but is referenced via import or ///<reference path="..." /> from a file that is included in tsconfig.json). In order to have them compiled, you need to explicitly mention those files in node_modules directory. For instance, if you are using a package my_package that contains typescript sources, you can add a key {"include": ["node_modules/my_package/**/*.ts"]} to your tsconfig.

Using closure compiler primitives

Certain JS expressions, such as goog.define(...) or goog.reflect.objectProperty(...), get special treatment from Closure Compiler. In order to use them, you need access to the goog variable or the export object of goog.reflect closure library module.

In order to access goog, first include a triple slash directive that points to a base.d.ts file that comes with the npm package.

///<reference path="node_modules/@tscc/tscc/third_party/closure_library/base.d.ts" >

The exact path may differ in your configuration. This file contains a declaration for a module "goog:goog", so you can now write

import * as goog from 'goog:goog'

to obtain a reference to the goog object. In order for this to work, the imported namespace's name should be goog as in above. As a matter of good practice, it'd better not to use goog as a variable name unless it is the closure compiler's goog object.

Similarly, to use goog.reflect, reference reflect.d.ts, and then write

import * as googReflect from 'goog:goog.reflect';

rollup-plugin-tscc will wire these module to an appropriate 'polyfill' modules so that runtime behaviors are unchanged.

Things to know

Closure compiler handles modern javascript natively

Closure compiler is capable of minifying modern javascript up to ECMASCRIPT 2019. If you only support modern environments, you can set closure compiler output langauge to ES6 or higher, it will provide smaller output in general.

Use declare interface to prevent property name renaming

Often you will need to prevent closure compiler renaming certain property names. Since you are writing typescript, such a property name will be a part of a certain interface. Add declare to that interface declaration. This does not produce additional meanings in typescript, but it will inform tsickle to create externs for the type so that properties of the interface are not renamed by closure compiler. Check out the tsickle's documentation.

Sourcemaps

In order to enable sourcemaps, enable compilerOptions.sourceMap flag in tsconfig.json. Then TSCC will configure closure compiler to emit appropriate sourcemaps.

Using prebuilt closure compiler images

By default, tscc command will use the java version of the compiler, which requires java to exist in PATH environment variable. Platform specific binary images are available in npm: google-closure-compiler-windows, google-closure-compiler-osx, google-closure-compiler-linux, and these are optional dependency of @tscc/tscc package. If you install one of them, tscc command will use it and it will provide significantly faster compile time in most cases.

Rules imposed by closure compiler and tsickle

Although TSCC tries to hide closure compiler specifics as much as it can, it's good to have some knowledge on it:

• Read the official documentation in order to get used to some notions used.
• Not all code works directly with closure compiler (even if it is well-annotated). Read about compiler assumptions from their wiki; Basically, you should not use some dynamic nature of JS (the bad part!). Below are some common situations.
  • Do not access an object's property with a string literal, as closure compiler won't try to rename it. If you access foo.bar in your code and also do foo["bar"] at another part of the code, closure compiler may rename foo.bar to something like foo.a whereas the latter to foo.bar, so it will break the code.
  • Circular references of Javascript modules are not allowed.
  • Output module spec must have a single root module, making it a connected tree.Ref
• Tsickle officially states that it is still in experimental phase, and there are some caveats.
  • Tsickle does not support annotation of all typescript types. For example, it does not convert indexed properties of Typescript to closure type, so if an interface is declared with a property, such an interface won't be preserved -- keep an eye on tsickle warnings about unknown types. A good news is that closure compiler is still able to guess unknown types in most of cases, so it does not break the output code often.
  • TS namespaces are not converted to something like those in closure library, so it does not benefit from closure compiler's property flattening. (Apparently google internally prevents use of namespaces.)
• Some objects are present in Typescript but not in closure compiler, so sometimes you may need to provide externs to those manually.

Motivation

This project came out from the experience I have had with developing several Javascript apps, as frontend projects, browser extensions, and userscripts injected into client's browsers. In many cases "content script" are evaled, so the source holds a string form of a JS code, so there was a rather strong motivation for squizing bundle size as much as one can in order to reduce client's memory footprint. Closure tools, albeit not "trendy", was the best tool for it -- the compiler is simply the best, Closure Templates directly compiles into JS and required runtime libraries are extremely small, and Closure Stylesheets provides class name shortening. However, incorporating all of these and at the same time providing an alternative build for debugging required a lot of work due to lack of support and community tooling.

On the other hand, currently most of available tooling using tsickle and closure compiler is limited to angular community. Tsickle is integrated into Angular's compiler and it provides some angular-specific code transformations (they are not enabled in TSCC). However, after all tsickle is a general-purpose transpiler. It seemed a pity that such a great tooling cannot benefit much broader audiences.

TSCC is meant to provide a framework-agnostic tooling that can be used to bridge this gap.

Milestones

• Integration with Closure Templates and Closure Stylesheets. Both tools produce Javascript sources that are meant to be consumed by Closure Compiler. As separate companion packages tscc-templates and tscc-styles, it will be possible to pipe these intermediate output to closure compiler, and produce typescript module declaration files that will provide type information of templates.
• Providing an ergonomic API for using closure-annotated JS files together with transpiled TS files.
• Providing an API for returning gulp stream.