lib/waterfall.js
function waterfall (tasks, callback) {
    callback = once(callback);
    if (!Array.isArray(tasks)) return callback(new Error('First argument to waterfall must be an array of functions'));
    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([]);
}
function waterfall (tasks, callback) {
    callback = once(callback);
    if (!Array.isArray(tasks)) return callback(new Error('First argument to waterfall must be an array of functions'));
    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([]);
}
function waterfall ( tasks , callback ) { callback = once ( callback ) ; if ( ! Array . isArray ( tasks ) ) return callback ( new Error ( 'First argument to waterfall must be an array of functions' ) ) ; 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 ( [ ] ) ; }
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's
callback. Invoked with (err, [results]).
@returns undefined
@example

async.waterfall([
function(callback) {
callback(null, 'one', 'two');
},
function(arg1, arg2, callback) {
// arg1 now equals 'one' and arg2 now equals 'two'
callback(null, 'three');
},
function(arg1, callback) {
// arg1 now equals 'three'
callback(null, 'done');
}
], function (err, result) {
// result now equals 'done'
});

// Or, with named functions:
async.waterfall([
myFirstFunction,
mySecondFunction,
myLastFunction,
], function (err, result) {
// result now equals 'done'
});
function myFirstFunction(callback) {
callback(null, 'one', 'two');
}
function mySecondFunction(arg1, arg2, callback) {
// arg1 now equals 'one' and arg2 now equals 'two'
callback(null, 'three');
}
function myLastFunction(arg1, callback) {
// arg1 now equals 'three'
callback(null, 'done');
}
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 .