A practical guide to building a dependency injection container in vanilla JavaScript without TypeScript, decorators, or runtime reflection. The approach stores dependency metadata directly on class constructors using private Symbols, supports singleton, scoped, and transient lifetimes, and uses object-based constructor injection. The tutorial walks through implementing the component helper, the container itself, circular dependency detection, request scopes, and applies the pattern to a DDD-style shopping cart application with repositories, application services, and a composition root.
Table of contents
Why Constructor Inspection Doesn’t WorkA Different ApproachCreating a ComponentChoosing Dependency TokensBuilding the ContainerResolving DependenciesDetecting Circular DependenciesWhy Constructor Parameters Are Passed as an ObjectAdding Request ScopesApplying the Container to a Real ProjectA Simple Value ObjectBuilding the AggregateTurning the Application Service into a ComponentRegistering Infrastructure ComponentsBuilding the Composition RootRunning the ApplicationWhy This Approach WorksBenefitsLimitationsFinal Thoughts4.7K Impressions