"Since the callback for each passes one parameter, so let's see this in action." 3:14 has thrown me off a little

Question

Hi guys,

Can't seem to grasp this code snippet properly, despite what Andrew is saying at 3:14:

var profile = require("./profile.js");
var users = process.argv.slice(2);
users.forEach(profile.get);

First line is fine, we are requiring from profile.js.
Second line is fine, we are just slicing the argv array at the index where our usernames will be entered

However I am unclear on how the forEach is working? It requires a callback function, which is fine; we call the get function in our profile file. However we have a 'username' argument on that function but we aren't supplying anything in users.forEach(profile.get);

How does the program pass through our username arguments to get(username)? I must be missing something really obvious here, perhaps?

Thanks, James.

Answer 1 · 2016-11-03T18:40:08Z

November 3, 2016 6:40pm

You are correct in saying that there is an argument on that function. But you're not calling the function, your passing the function as a callback and allow the forEach function to call the function with the appropriate arguments.

Here is a basic example:

//Our very own (and basic) implementation of forEach
Array.prototype.customForEach = function(callback) {
    for (var i = 0; i < this.length; i++) {

        //Here, we're invoking the function we passed in
        callback(this[i]);
    }
}


//A function that accepts a number and prints it out
function printNumbers(n) {
    console.log(n);
}


//The arrray we're working with
var arr = [1, 2, 3, 4, 5];


//Here we're calling our custom forEach and passing the function to it
//(NOT calling it)
arr.customForEach(printNumbers);

Welcome to the Treehouse Community

Looking to learn something new?

James Barrett

James Barrett

"Since the callback for each passes one parameter, so let's see this in action." 3:14 has thrown me off a little

1 Answer

Thomas Nilsen

Thomas Nilsen