Java script : .map()

ITERATORS

.map()

In the previous exercise, we called the .forEach() method and learned that it returns undefined. It also does not change the array it is called upon. What if we do want to change the contents of the array? We can use .map()!

let numbers = [1, 2, 3, 4, 5]; 

let bigNumbers = numbers.map(function(number) {
  return number * 10;
});

1. The first line is an array of numbers.
2. let bigNumbers = numbers.map creates a new array, bigNumbers, in which the returned values of the .map() method will be saved and calls the .map() method on the numbers array.
3. (function(number) { creates a function that takes a single parameter, number, and opens the block of code for that function.
4. return number * 10; is the code we wish to execute upon each element in the array. This will save each value from the numbers array, multiplied by 10, to the bigNumbers array.
5. }); closes the function code block and .map() method in that order.

The syntax for .map() is almost the same as the syntax for .forEach(), with one important change. Notice that directly before the function call, the code reads, let bigNumbers =. This is because .map() returns a new array with elements that have been modified by the code in its block. bigNumbersis the new array in which the method will save the values.

.map() can also be written with arrow function syntax.

let numbers = [1, 2, 3, 4, 5]; 
let bigNumbers = numbers.map(numbers => numbers * 10);

1.

On line 4, use .map() to create a new array called secretMessage that returns the first character of each string in the animals array.

Create the variable using let and write out the method call using function; you'll refactor to arrow function syntax in a later step.

2.

Use .map() to divide all the numbers in bigNumbers by 100. Save the returned values to a new array called smallNumbers, declared with let.

3.

Refactor the method call from Step 1 using arrow function syntax