• Create and manipulate objects
• Create and manipulate arrays
• Create and call functions
• Create and use variables
• Use string methods
• Use number methods

Before we dive into this lab, we need to tell you something: remember how easy it was to iterate over an array with a for or a while loop? Well, it's nearly as easy to iterate over an object in the same way. (Remember, arrays are essentially fancy objects — it makes sense that iteration would be similar.)

But objects don't have sequential indexes like arrays do, so we need another way of getting the keys. Luckily, that's exactly what Object.keys() is for!

var meals = {
  breakfast: 'oatmeal',
  lunch: 'tuna',
  dinner: 'spaghetti'
}

var mealNames = Object.keys(meals)

for (var i = 0, l = mealNames.length; i < l; i++) {
  console.log(`I ate ${meals[mealNames[i]]} for ${mealNames[i]}!`)
}

// I ate oatmeal for breakfast!
// I ate tuna for lunch!
// I ate spaghetti for dinner!

But this is a little verbose and sort of hard to read: we have to get the name of the meal using mealNames[i] and then use that name as a key in the object meals to get the food for that meal (meals[mealNames[i]]). Gross.

There's a (slightly) better way! JavaScript has a special loop, called for...in, that makes iterating over objects a bit easier:

var meals = {
  breakfast: 'oatmeal',
  lunch: 'tuna',
  dinner: 'spaghetti'
}

for (var mealName in meals) {
  console.log(`I ate ${meals[mealName]} for ${mealName}!`)
}

Much better.

NOTE: You can use for...in loops with arrays, too, but the variable that you get will just be the index (in order), so this particular loop is usually used with objects.

• We've given you a function setCart() which takes one argument, an array, and sets cart (a variable that we've provided) to that array.

• We've also given you a function total which does not accept any arguments. It iterates over the items in cart and adds up their prices, then returns the total.

• Define a global variable (use var at the top level) called cart. Initialize it as an empty array.

• Define a function getCart that takes no arguments and returns the cart.

• Define a function addToCart. This function should accept one argument, the item the user wants to purchase. This function should automatically set a price for this item by generating a random number between 0 and 100. (Hint: Math.random() generates a random number in [0, 1] (0 inclusive, 1 non-inclusive); Math.floor() rounds a number down to the nearest integer.) This function should add the item and the price as an object ({item: price}) to the cart array. This function should print out to the console <item> has been added to your cart. and return the cart.

• Define a function viewCart which does not accept any arguments. This function should loop over every item in cart to print out "In your cart, you have [item and price pairs].". If there isn't anything in your cart, the function should print out "Your shopping cart is empty.".

• Define a function removeFromCart which accepts one argument, the name of the item you wish to remove. If the item isn't in the cart, the function should print out "That item is not in your cart.". If the item is in your cart, it should remove the object from the cart array. Then return the cart. (HINT: Check each object's key to see if it matches the parameter, then remove it if it matches. You might find hasOwnProperty to be useful.)

• Define a function placeOrder which accepts one argument, a credit card number. If no argument is received, then the function should print out "We don't have a credit card on file for you to place your order.". If there is a credit card on file, the function should print out "Your total cost is $${total()}, which will be charged to the card ${cardNumber}.". The function should empty the cart array.

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