Loops & Iteration

Question 1

When looping through arrays, why is a for…of loop preferred over a standard for loop?

Answer 1

A for…of will loop over the array once without the need for setting increments or conditionals

Question 2

What is the full syntax of the forEach method?

Answer 2

The syntax of the forEach method, which is found on arrays:

arrayName.forEach((currentValue, index, array) ={

codeBlock of loop

})

Question 3

Does the forEach method for arrays take a callback?

Answer 3

Yes, the forEach method takes a callback.

Question 4

What are the three parameters for a forEach callback function?

Answer 4

currentValue, index, array

Question 5

What is the most common way we would see a forEach method?

Answer 5

Looping over an array when we are concerned with the currentValue only.

arrayName.forEach((currentValue) => {doSomething with currentValue})

Question 6

Which is faster, a forEach method call or a for…of loop?

Answer 6

The for…of loop is faster.

Question 7

How can we refer to a variable name when looking at iteration syntax?

Answer 7

The variable name can also be called the “Identifier”

Question 8

What is the returned value for a .forEach method call?

Answer 8

It is always undefined, we need to do something with the function product in the callback itself

Question 9

How does the .forEach method work?

Answer 9

.forEach loops through the array and executes the callback function for each element. During each execution, the current element is passed as an argument to the callback function.

Question 10

Are .forEach and for…of iteration methods equivilent?

Answer 10

No, .forEach does not work well with Async/Await and some edge cases. for…of iteration can make it difficult to get the index value and can’t be chained.

Question 11

What is the difference between .map and .forEach?

Answer 11

.map creates a new array with the results of the callback function provided.

Question 12

How is the .filter method used?

Answer 12

Use the .filter method to iterate over an array and then create a new array with elements that return true to the callback function

Question 13

Does the .filter method create a new array?

Answer 13

Yes, it creates a new array out of elements that return true in the callback function.

Question 14

What does the method .findIndex return?

Answer 14

It will return the index of the first element in an array that evaluates to true in the callback function.

Question 15

What will .findIndex return if no elements evaluate to true in the callback function?

Answer 15

.findIndex will return -1 if no elements evaluate to true in the callback function.

Question 16

What is the .reduce method used for in JavaScript?

Answer 16

The .reduce method allows us to simplify an input array based on the code block contained within the callback.

It is often used to sum an array but can be used to flatten an array (with concat).

Question 17

What is the syntax of a basic .reduce method call?

Answer 17

arrayName.reduce((accumulator, currentValue) => {

return accumulator + currentValue
}

Question 18

How do we set an initial value for a .reduce method call?

Answer 18

We pass in the initial value as the second parameter to the .reduce method, after the callback function.

Question 19

When must we supply an initial value to a .reduce method call?

Answer 19

We must supply an initial value to a .reduce method call when we are using reduce on an array of objects.

Question 20

What does the .map method do for us?

Answer 20

The .map method takes each value of an array, performs a callback function on the value, and creates a new array with that value.

Question 21

What is the typographical representation of the Rest or Spread operator?

Answer 21

( … ) is the typographical representation of the Rest or Spread operator