Child containers

A child container is a DI container that inherits all providers and singletons from its parent (or any ancestor). However, it also allows you to override specific providers or define new ones independently.

Example

import { Container } from "@needle-di/core";

import { LOGGER, MyLogger, OtherLogger } from "./logger";

const parent = new Container();
const child1 = parent.createChild();
const child2 = parent.createChild();

parent.bind({ provide: LOGGER, useClass: MyLogger });
child2.bind({ provide: LOGGER, useClass: OtherLogger });

const loggerA = parent.get(LOGGER); // `MyLogger`
const loggerB = child1.get(LOGGER); // `MyLogger` (same instance as parent)
const loggerC = child2.get(LOGGER); // `OtherLogger`

Rules and behaviour

• Singletons are shared with child containers (or any descendant) unless explicitly overridden.
• Singletons are created in the container where they were first bound, even if they are accessed from a child container.

NOTE

If you bind a multi-provider in a child container, its singletons will not be merged with those from the parent. This is a current limitation, but if you have a strong use case, feel free to submit an issue.