option-t/esm/maybe/xor.js

A toolkit of Nullable/Option/Result type implementation in ECMAScript. Their APIs are inspired by Rust's `Option<T>` and `Result<T, E>`.

import { isNotNullOrUndefined } from './maybe.js';
/**
 *  Return one of this pattern:
 *
 *  1. a=others, b=null|undefined => _a_
 *  2. a=null|undefined, b=others => _b_
 *  3. Others => `undefined`
 */
export function xorForMaybe(a, b) {
    const aIsSome = isNotNullOrUndefined(a);
    const bIsSome = isNotNullOrUndefined(b);
    if (aIsSome && !bIsSome) {
        return a;
    }
    if (!aIsSome && bIsSome) {
        return b;
    }
    // XXX: We can choose both `null` and `undefined`.
    // But we return `undefined` to sort with [Optional Chaining](https://github.com/TC39/proposal-optional-chaining)
    return undefined;
}