cache-chain.js

/**
 * @template T1
 */
class CacheChain {
    /**
     * @param {function():*|function():CacheChain<*>} fn
     */
    constructor(fn) {
        this._fn = fn;

        this._cache = null;
    }

    /**
     * @template T1
     * @template T2
     * @param {function(T1):T2|function(T1):CacheChain<T2>}fn
     * @return {CacheChain<T2>}
     */
    then(fn) {
        if (!this._cache) {
            this._cache = this._fn();
        }

        if (this._cache instanceof CacheChain) {
            return this._cache.then(fn);
        } else {
            Object.freeze(this._cache);
            return new CacheChain(() => fn(this._cache));
        }
    }

    /**
     * @deprecated
     * @return {T1}
     */
    get value() {
        let res = null;

        this.then((data) => {
            res = data;
        }).then(_ => _);

        return res;
    }
}

export default CacheChain;
// @desc
// const c = new CacheChain(() => ({a:1, b:2}));
// const cc1 = c.then((obj) => {console.log(obj); return obj?.a});
// const cc2 = c.then((obj) => {console.log(obj); return obj?.b});
// cc1.then((a) => console.log(a));
// cc2.then((b) => console.log(b));
//
// result
// c cache
// cc1 cache {a:1, b:2}
// cc2 cache {a:1, b:2}