Elegant Error Handling Code Samples

left-with-chain.js

/**
 *Left represents the sad path.
 */
class Left {
    constructor(val) {
        this._value = val;
    }

    map() {
        // Left is the sad path
        // so we do nothing
        return this;
    }

    join() {
        // On the sad path, we don't
        // do anything with join
        return this;
    }

    chain() {
        // Boring sad path,
        // do nothing.
        return this;
    }

    toString() {
        const str = this._value.toString();
        return `Left(${$str})`;
    }
}

right-with-join.js

/**
 * Right represents the happy path
 */
class Right {
    constructor(val) {
        this._value = val;
    }

    map(fn) {
        return new Right(
            fn(this._value)
        );
    }

    join() {
        if ((this._value instanceof Left)
            || (this._value instanceof Right)) {
            return this._value;
        }
        return this;
    }

    chain(fn) {
        return fn(this._value);
    }

    toString() {
        const str = this._value.toString();
        return `Right(${str})`;
    }
}