Summary: Going Loopy Over Arrays

Key points

• The spread operator can be applied to strings to spread them into an array containing each character as a separate item.
• Iteration methods loop through every value in a collection and apply an operation to each value.
• JavaScript has a number array of methods that apply a callback to every item in the array.
• The forEach() method applies the code in the callback for every item in the array.
• The map() method returns a new array by applying the code in the callback to every item in the array.
• The reduce() method returns a single value by applying an accumulator function defined in the callback to every value in the array—for example, adding up all the values in the array.
• The filter() method returns a new array containing only the values from the original array that match the criteria defined in the callback.
• The find() method returns the first item in an array that matches the criteria given in the callback.
• The every() method returns true if every item in the array matches the criteria given in the callback. Otherwise, it returns false.
• The some() method returns true if any item in the array matches the criteria given in the callback. It returns false if none of the items in the array match the criteria.
• We can iterate over objects using a for–in loop that will give us access to each property in the object.
• The Object.keys(), Object.values() and Object.entries() methods will return an array of an object’s keys, values, or key–value pairs respectively.

After the quiz and challenge, we’ll be getting functional with functions.