How do you properly format the queue for lesson 165?

#1

I am trying to make sure I understand the core concepts of this exercise and value the educational journey of each individual so I am posting here instead of on the facebook group.

This question pertains to stand in line lesson 165.

Here is the code:

------------------------------------------------------
function nextInLine(arr, item) {
  // Your code here
 arr = ["chicken", "turkey", "sausage"];
 item = 1;
 arr.push(item);
 var removed = arr.shift(0);
 return removed;
}
------------------------------------------------------------------------
// Test Setup
var testArr = [1,2,3,4,5];

// Display Code
console.log("Before: " + JSON.stringify(testArr));
console.log(nextInLine(testArr, 6)); // Modify this line to test
console.log("After: " + JSON.stringify(testArr));

Why does the above not work, in comparison to the below:

(answer from the website)

function nextInLine(arr, item) {
  // Your code here
  arr.push(item);
  var removed = arr.shift();
  return removed;  // Change this line
}
#2

You are overwriting arr and item inside your function.

#3

Can you point out where it was written before?

#4

Not sure what you mean. But if you compare your code with the solution, you see that you have two extra lines:

arr = ["chicken", "turkey", "sausage"];
item = 1;

But arr and item are passed to the function as parameters. So no matter what you pass to the function it will always return the same, because you overwrite those values.

#5

By overwrite you mean that it was already written before (writing again when not neccesary?)

#6

I guess arr and item were defined somewhere else (where I cannot see that part of the code)

#7

arr and item get their values by calling the function with certain parameters. E.g. running nextInLine([1,2,3,4],2) will run the function nextInLine and give arr the value of [1,2,3,4] and item the value of 2.

The only thing the tests do, is running the function with certain parameters and then check if the return value is what it should be.

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#8

I see that removing those works.

In a different exercise, I was asked to define a variable inside a function first.

I guess I’m not sure why these variables in the currently addressed exercise do not need to be defined (or if they are defined somewhere else) .

Here is the example from a different exercise where I had to define the variable first - exercise Global Scope and Functions:

-------------------------------------------------
// Declare your variable here
var myGlobal = 10;
-------------------------------------------------
function fun1() { 
  // Assign 5 to oopsGlobal Here
  oopsGlobal= 5; console.log(oopsGlobal);}
fun1();
// Only change code above this line
function fun2() {
  var output = "";
  if (typeof myGlobal != "undefined") {
    output += "myGlobal: " + myGlobal;
  }
  if (typeof oopsGlobal != "undefined") {
    output += " oopsGlobal: " + oopsGlobal;
  }
  console.log(output);
}
#9

I thought standard practice was to define variables first - like I said, it’s not about the answer…I’m trying to make sure I understand each concept.

#10

Have a look at this challenge: https://www.freecodecamp.org/challenges/passing-values-to-functions-with-arguments. You can see that you don’t need to define a and b.

#11

The point of a function is to be a reusable bit of code. So for example if you want something that adds two numbers:

function add(a, b) {
  return a + b;
}

You don’t write

function add(a, b) {
  var a = 1;
  var b = 2;
  return a + b;
}

Because that completely defeats the point of using a function. If you do that, it then makes no difference if you’d like to add 4 and 5, the function will always just add 1 and 2.

The earlier challenges use global variables because it’s easier to understand for simple things: it means everything is explicit while you’re learning the basics. Once you’re past there, they aren’t good practice in 99.999999% of cases.

EDIT: you wanted to know where the values come from. There are a set of tests that run when you hit go. They run the function with different values, and check if each set of input values returns what was expected. The function should work for any value that matches the expected inputs

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