@ayonli/jsext/esm/external/check-iterable/index.js

A JavaScript extension package for building strong and modern applications.

if (!Symbol.asyncIterator) {
    // @ts-ignore
    Symbol.asyncIterator = Symbol("Symbol.asyncIterator");
}

/**
 * Checks if the given object is an IteratorLike (implemented `next`).
 * @param {any} obj
 * @returns {obj is { [x: string | symbol]: any; next: Function }}
 */
function isIteratorLike(obj) {
    // An iterable object has a 'next' method, however including a 'next' method
    // doesn't ensure the object is an iterator, it is only iterator-like.
    return typeof obj === "object"
        && obj !== null
        && typeof obj.next === "function";
}

/**
 * Checks if the given object is an IterableIterator (implemented both
 * `@@iterator` and `next`).
 * @param {any} obj
 */
function isIterableIterator(obj) {
    return isIteratorLike(obj)
        && typeof obj[Symbol.iterator] === "function";
}

/**
 * Checks if the given object is an AsyncIterableIterator (implemented
 * both `@@asyncIterator` and `next`).
 * @param {any} obj
 * @returns {obj is AsyncIterableIterator<any>}
 */
function isAsyncIterableIterator(obj) {
    return isIteratorLike(obj)
        && typeof obj[Symbol.asyncIterator] === "function";
}

/**
 * Checks if the given object is a Generator.
 * @param {any} obj
 * @returns {obj is Generator}
 */
function isGenerator(obj) {
    return isIterableIterator(obj)
        && hasGeneratorSpecials(obj);
}

/**
 * Checks if the given object is an AsyncGenerator.
 * @param {any} obj
 * @returns {obj is AsyncGenerator}
 */
function isAsyncGenerator(obj) {
    return isAsyncIterableIterator(obj)
        && hasGeneratorSpecials(obj);
}

/**
 * @param {any} obj 
 */
function hasGeneratorSpecials(obj) {
    return typeof obj.return === "function"
        && typeof obj.throw === "function";
}

export { isAsyncGenerator, isAsyncIterableIterator, isGenerator, isIterableIterator, isIteratorLike };
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