Systemjs

SystemJS is a dynamic dependency manager and universal module loader that resolves and executes JavaScript modules across different browser and server environments. It functions as an import map polyfill, mapping bare module specifiers to absolute URLs to manage dependencies without requiring a build step.

The project provides a system for integrating diverse formats, including AMD and global scripts, into a modern ES module workflow. It enables browser module polyfilling for environments that lack native support for ES modules and import maps, and it allows for dynamic runtime hot-reloading by managing the module registry.

Its capabilities cover custom asset loading for non-JavaScript files such as WebAssembly, CSS, and JSON. The loader also supports modular dependency management, the execution of modules in Node.js, and the ability to verify module integrity using cryptographic hashes.

Features

Dynamic Module Loaders - Functions as a universal module loader that resolves and executes JavaScript modules across different environments.

Module Resolvers - Resolves bare module specifiers to absolute URLs using configurable import maps.

ES Module Support - Functions as a dynamic loader that resolves and executes ES modules across different browser and server environments.

URL Resolvers - Maps bare module names to specific absolute or relative URLs using a mapping configuration.

Resolution and Mapping Systems - Uses a configurable lookup table to resolve bare module specifiers into absolute URLs at runtime.

Import Map Configurations - Provides mapping configurations that resolve module import paths to specific network locations based on the importer's context.

Dynamic Dependency Managers - Acts as a runtime registry that fetches and manages the lifecycle of JavaScript modules and non-JS assets.

Module Management - Fetches modules by name or URL and resolves them to their namespace values.

Import Maps - Implements an import map polyfill that resolves module specifiers to specific URLs without requiring a build step.

Hot Module Reloaders - Manages the internal module registry to facilitate runtime hot-reloading and memory cleanup.

ES Module Integrations - Replicates modern ES module semantics in older browsers using a specialized polyfill format.

Module Format Polyfills - Emulates ES module semantics by wrapping code in registration functions to provide module support in legacy environments.

Polyfill Module Declarations - Provides a polyfill format for registering modules and declaring their dependencies and exports.

Universal Module Loaders - Integrates diverse module formats, including AMD and global scripts, into a modern ES module workflow.

Dynamic Imports - Implements a contextual import function to enable asynchronous module loading during runtime.

Module-Based Registries - Maintains a centralized registry of loaded module namespaces to ensure single-instance execution and dependency sharing.

Modular Dependency Management - Maps bare module specifiers to absolute URLs to simplify how libraries are referenced and resolved at runtime.

View-to-URL Mapping - Maps bare module specifiers to specific URLs using configuration to simplify dependency references.

Polyfills - Provides modern module loading and import map capabilities to older browsers that lack native support.

Legacy Module Format Support - Provides runtime support for loading and executing modules defined via the Asynchronous Module Definition format.

Asset Loading and Resolution - Integrates non-JavaScript assets like WebAssembly, CSS, and JSON as first-class modules.

Runtime Loader Hooks - Provides custom hooks to modify how modules are resolved and fetched during the loading process.

Import Map Loading - Retrieves module mapping configurations from external sources using programmable fetch hooks.

Async-Await Flow Control - Executes modules asynchronously by supporting top-level await in the module entry function.

Module Lifecycle Managers - Manages the lifecycle of loaded modules, including the ability to remove them from the registry for code reloading.

JSON Module Imports - Treats JSON files as first-class modules for direct use as default exports within JavaScript.

Scoped Resolutions - Allows applying different module mappings based on the importing file path to support multiple dependency versions.

Legacy Format Integration - Integrates diverse legacy formats, including AMD and global scripts, into a modern ES module workflow.

Legacy Module Adapters - Integrates legacy module patterns like AMD and global scripts into a modern ES module workflow.

Non-JavaScript Asset Imports - Enables the integration of JSON, CSS, and WebAssembly binaries as standard modules.

Parallel Dependency Loading - Prevents network waterfalls by defining the dependency tree upfront to fetch all lazy modules simultaneously.

Concurrent Dependency Resolution - Implements concurrent fetching of the full dependency graph to prevent sequential network request waterfalls.

Module Loaders - Overrides the default network request mechanism to transform module source code before it is executed.

Import Assertions - Implements import assertions to let the loader determine the correct format for non-JavaScript assets.

Hook-Based Extension Frameworks - Provides a programmable hook-based pipeline to intercept and customize module resolution, fetching, and instantiation.

Module Pipeline Interceptors - Intercepts the resolution, fetching, instantiation, and execution of modules to support custom file formats.

Constructable Stylesheets - Provides the ability to load CSS as modules using constructable stylesheets for integrated styling.

Browser Scripting Tools - Uses asynchronous hooks to customize the creation and loading of scripts in the browser.

Global Script Registrations - Imports traditional non-module scripts and exposes their global variables as default exports.

WebAssembly Module Loaders - Loads WebAssembly binaries as modules that can maintain imports and exports.

Build Tools - Dynamic module loader for modern browser environments.

Module Loaders - Universal loader for ES6, AMD, and CommonJS.

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Features

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