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        <h1 class="page-title">waterfall.js</h1>
        

        



    
    <section>
        <article>
            <pre class="prettyprint source linenums"><code>import once from &apos;./internal/once.js&apos;
import onlyOnce from &apos;./internal/onlyOnce.js&apos;
import wrapAsync from &apos;./internal/wrapAsync.js&apos;
import awaitify from &apos;./internal/awaitify.js&apos;

/**
 * Runs the `tasks` array of functions in series, each passing their results to
 * the next in the array. However, if any of the `tasks` pass an error to their
 * own callback, the next function is not executed, and the main `callback` is
 * immediately called with the error.
 *
 * @name waterfall
 * @static
 * @memberOf module:ControlFlow
 * @method
 * @category Control Flow
 * @param {Array} tasks - An array of [async functions]{@link AsyncFunction}
 * to run.
 * Each function should complete with any number of `result` values.
 * The `result` values will be passed as arguments, in order, to the next task.
 * @param {Function} [callback] - An optional callback to run once all the
 * functions have completed. This will be passed the results of the last task&apos;s
 * callback. Invoked with (err, [results]).
 * @returns {Promise} a promise, if a callback is omitted
 * @example
 *
 * async.waterfall([
 *     function(callback) {
 *         callback(null, &apos;one&apos;, &apos;two&apos;);
 *     },
 *     function(arg1, arg2, callback) {
 *         // arg1 now equals &apos;one&apos; and arg2 now equals &apos;two&apos;
 *         callback(null, &apos;three&apos;);
 *     },
 *     function(arg1, callback) {
 *         // arg1 now equals &apos;three&apos;
 *         callback(null, &apos;done&apos;);
 *     }
 * ], function (err, result) {
 *     // result now equals &apos;done&apos;
 * });
 *
 * // Or, with named functions:
 * async.waterfall([
 *     myFirstFunction,
 *     mySecondFunction,
 *     myLastFunction,
 * ], function (err, result) {
 *     // result now equals &apos;done&apos;
 * });
 * function myFirstFunction(callback) {
 *     callback(null, &apos;one&apos;, &apos;two&apos;);
 * }
 * function mySecondFunction(arg1, arg2, callback) {
 *     // arg1 now equals &apos;one&apos; and arg2 now equals &apos;two&apos;
 *     callback(null, &apos;three&apos;);
 * }
 * function myLastFunction(arg1, callback) {
 *     // arg1 now equals &apos;three&apos;
 *     callback(null, &apos;done&apos;);
 * }
 */
function waterfall (tasks, callback) {
    callback = once(callback);
    if (!Array.isArray(tasks)) return callback(new Error(&apos;First argument to waterfall must be an array of functions&apos;));
    if (!tasks.length) return callback();
    var taskIndex = 0;

    function nextTask(args) {
        var task = wrapAsync(tasks[taskIndex++]);
        task(...args, onlyOnce(next));
    }

    function next(err, ...args) {
        if (err === false) return
        if (err || taskIndex === tasks.length) {
            return callback(err, ...args);
        }
        nextTask(args);
    }

    nextTask([]);
}

export default awaitify(waterfall)
</code></pre>
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