async waterfall getting Typeerror, nextcallback is not a function

Question

async.waterfall([1,2,3,4].map(function (arrayItem) {
        return function (lastItemResult, nextCallback) {
            // same execution for each item in the array
            var itemResult = (arrayItem+lastItemResult);
            // results carried along from each to the next
            nextCallback(null, itemResult);
        }}), function (err, result) {
        // final callback
    });

so i am new to async and trying a simple example but getting this error, what is wrong with this method TypeError: nextCallback is not a function

what is wrong with the code above?

Answer 1

According to the documentation the signature of a first function should be function (callback) and not function (arg1, callback).

You can patch your function this way.

return function (lastItemResult, nextCallback) {
    if (!nextCallback) {
      nextCallback = lastItemResult;
      lastItemResult = 0;
    }

    // same execution for each item in the array
    var itemResult = (arrayItem+lastItemResult);
    // results carried along from each to the next
    nextCallback(null, itemResult);
};