option-t/esm/undefinable/operators/filter.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 { isNotUndefined } from '../core/undefinable.js';
/**
 *  Returns `undefined` if the _input_ is `undefined`,
 *  otherwise calls _predicate_ with the _input_ `T` and returns:
 *
 *      * `T` if _predicate_ returns `true`.
 *      * `undefined` if _predicate_ returns `false`.
 */
export function filterForUndefinable(input, predicate) {
    if (isNotUndefined(input)) {
        const ok = predicate(input);
        if (ok) {
            return input;
        }
    }
    return undefined;
}
/**
 *  Returns `undefined` if the _input_ is `undefined`,
 *  otherwise calls _predicate_ with the _input_ `T` and returns:
 *
 *      * The input value as `U` if _predicate_ returns `true` which means that _predicate_ says the input value is U.
 *      * `undefined` if _predicate_ returns `false`.
 *
 *  Please use {@link filterForUndefinable} generally if you don't have to narrow the type.
 */
export function filterWithEnsureTypeForUndefinable(input, predicate) {
    if (isNotUndefined(input)) {
        if (predicate(input)) {
            const result = input;
            return result;
        }
    }
    return undefined;
}