iteragain/dist/esm/arrayLike.js

Javascript Iterable/Iterator/Generator-function utilities.

import seekable from './seekable';
// TODO: possible add an overload for passing in a seekable to begin with, so that the maxLength param could be used.
/**
 * @description Creates a proxy object that allows for readonly array-like access to the elements of the input iterator. Some
 * important things to note are:
 * - `length` will always be the length of the internal cache, not the length of the final
 * iterated values.
 * - `Symbol.iterator` will always iterate over the entire input iterator, not just the cached values.
 * - Negative indices are allowed, and will seek backwards from the end of the internal cache.
 * @param arg The input iterator or iterable.
 */
export function arrayLike(arg) {
    const it = seekable(arg);
    // eslint-disable-next-line no-undef
    return new Proxy([], {
        get(target, prop) {
            if (prop === 'length')
                return it.elements.length;
            else if (prop === Symbol.iterator) {
                it.seek(0);
                return it[Symbol.iterator].bind(it);
            }
            else if (prop && prop in it.elements) {
                const value = target[prop];
                if (typeof value === 'function')
                    return value.bind(it.elements);
            }
            const index = Number(prop);
            if (!isNaN(index)) {
                it.seek(index);
                return it.next().value;
            }
            return undefined;
        },
        has(_, prop) {
            return prop in it.elements;
        },
        ownKeys() {
            return Object.keys(it.elements).concat('length');
        },
        getOwnPropertyDescriptor(_, prop) {
            return Object.getOwnPropertyDescriptor(it.elements, prop);
        },
        set(_, prop) {
            throw new TypeError(`Cannot assign to read only property '${prop.toString()}' of ArrayLikeIterator.`);
        },
        deleteProperty(_, prop) {
            throw new TypeError(`Cannot delete property '${prop.toString()}' of ArrayLikeIterator.`);
        },
        defineProperty(_, prop) {
            throw new TypeError(`Cannot define property '${prop.toString()}' of ArrayLikeIterator.`);
        },
    });
}
export default arrayLike;
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