di-lazy/build/index.mjs

Lazy instantiation of the class based on the first access to its reference

const NEVER_VALUE = Symbol('never');
const lazy = (ClassCtor, ...keys) => {
    let instance = NEVER_VALUE;
    const initKeys = new Set(keys);
    if (!initKeys.size) {
        throw new Error("di-lazy lazy no keys provided");
    }
    const activateInstance = (key, ...args) => {
        if (instance === NEVER_VALUE && initKeys.has(key)) {
            instance = new ClassCtor(...args);
            // @ts-ignore
            instance.init && instance.init();
        }
        return instance === NEVER_VALUE ? {} : instance;
    };
    class ClassReferer {
        constructor(...args) {
            const proxyInstance = new Proxy(this, {
                get(_, propKey, receiver) {
                    if (propKey === 'init') {
                        return;
                    }
                    const reference = activateInstance(propKey, ...args);
                    return Reflect.get(reference, propKey, receiver);
                },
                set(_, propKey, value, receiver) {
                    if (propKey === 'init') {
                        return false;
                    }
                    const reference = activateInstance(propKey, ...args);
                    return Reflect.set(reference, propKey, value, receiver);
                },
            });
            Object.setPrototypeOf(this, proxyInstance);
        }
        ;
    }
    function ClassActivator(...args) {
        return new ClassReferer(...args);
    }
    return ClassActivator;
};
/*
const LazyClass = lazy(class {
  constructor(...args: number[]) {
    console.log("CTOR", { args })
  }
  test = () => console.log("test")
}, "test");

const lazyInstance = new LazyClass(1, 2, 3);

console.log("Instance created");

lazyInstance.test();

console.log("Method executed")
*/

export { lazy };