ix/iterable/first.mjs

The Interactive Extensions for JavaScript

/**
 * Returns the first element of an iterable sequence that matches the predicate if provided, or undefined if no such element exists.
 *
 * @template T The type of the elements in the source sequence.
 * @param {Iterable<T>} source Source async-enumerable sequence.
 * @returns {(S | undefined)} The first element in the iterable sequence, or undefined if no such element exists.
 */
export function first(source, options) {
    const { ['thisArg']: thisArg, ['predicate']: predicate = () => true } = options || {};
    let i = 0;
    for (const item of source) {
        if (predicate.call(thisArg, item, i++)) {
            return item;
        }
    }
    return undefined;
}

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