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JavaScript Intro to Functions Lab

Objectives

  • Practice writing functions
  • Explain basics of working with strings
  • Explain the difference between return and logging
  • Practice using return and console.log()

Introduction

Welcome to the JavaScript functions lab! You'll notice a few new things in this lesson that we haven't encountered before. Don't worry, we'll walk you through them.

Even if you've walked through some of this material before, it's a good idea to review as we code-along — we're writing functions now, after all.

Code-Along

For now, open up index.js in your text editor. You should see, well, nothing. We'll fix that soon.

Now open up test/root.js. Hey, there's something! What's all of this stuff doing?

At the very top of the file, you'll see

global.expect = require('expect');

const babel = require('babel-core');
const jsdom = require('jsdom');
const path = require('path');

This might be a bit bewildering, but all we're doing is referencing different libraries that help us run your tests. A library is code that someone else (usually multiple someone elses) wrote for our use. Note that require won't work out of the box in the browser. We're actually running our tests in a different environment.

If you go to test/index-test.js, you'll see

describe('shout(string)', function() => {
  // there's stuff in here, too
})

describe is a function provided by our test runner (in this case, we're using Mocha) — it's basically a container for our tests.

Let's take a closer look at that describe():

describe('shout(string)', function() => {
  it('receives one argument and returns it in all caps', function() => {
    // we'll get to this in a sec
  })
})

These internal describe() calls are used for describing the functions that you're going to write. In this case, the test is saying, "Okay, I think there's going to be a function called shout, and it should take one argument (it doesn't actually matter what the argument is called, but string, is nice and specific, don't you think?). It should return that argument in all caps.

Finally, we have

expect(shout('hello')).toEqual('HELLO')

which says that it expects a call to shout() with the string 'hello' will equal the string 'HELLO'. This is the actual test — otherwise called a spec, expectation, or assertion — for this function. We can have more than one test per function, but let's start with this one.

Running the Tests

To run the tests, run learn test in the terminal in your Learn IDE. The first output you'll see will look like

> [email protected] test /Users/mbenton/Desktop/curriculum-team/junk/javascript-intro-to-functions-lab
> mocha -R mocha-multi --reporter-options spec=-,json=.results.json --timeout 10000



  shout(string)
    1) receives one argument and returns it in all caps

  whisper(string)
    2) receives one argument and returns it in all lowercase

  logShout(string)
    3) calls console.log() its one argument in all caps

  logWhisper(string)
    4) calls console.log() its one argument in all lowercase

  sayHiToGrandma(string)
    5) returns "I can't hear you!" if `string` is lowercase
    6) returns "YES INDEED!" if `string` is uppercase
    7) returns "I love you, too." if `string` is "I love you, Grandma."`


  0 passing (99ms)
  7 failing

  1) shout(string)
       receives one argument and returns it in all caps:
     ReferenceError: shout is not defined
      at Context.<anonymous> (test/index-test.js:4:5)
      at processImmediate (internal/timers.js:456:21)

  2) whisper(string)
       receives one argument and returns it in all lowercase:
     ReferenceError: whisper is not defined
      at Context.<anonymous> (test/index-test.js:10:5)
      at processImmediate (internal/timers.js:456:21)

  3) logShout(string)
       calls console.log() its one argument in all caps:
     ReferenceError: logShout is not defined
      at Context.<anonymous> (test/index-test.js:18:5)
      at processImmediate (internal/timers.js:456:21)

  4) logWhisper(string)
       calls console.log() its one argument in all lowercase:
     ReferenceError: logWhisper is not defined
      at Context.<anonymous> (test/index-test.js:30:5)
      at processImmediate (internal/timers.js:456:21)

  5) sayHiToGrandma(string)
       returns "I can't hear you!" if `string` is lowercase:
     ReferenceError: sayHiToGrandma is not defined
      at Context.<anonymous> (test/index-test.js:40:5)
      at processImmediate (internal/timers.js:456:21)

  6) sayHiToGrandma(string)
       returns "YES INDEED!" if `string` is uppercase:
     ReferenceError: sayHiToGrandma is not defined
      at Context.<anonymous> (test/index-test.js:44:5)
      at processImmediate (internal/timers.js:456:21)

  7) sayHiToGrandma(string)
       returns "I love you, too." if `string` is "I love you, Grandma."`:
     ReferenceError: sayHiToGrandma is not defined
      at Context.<anonymous> (test/index-test.js:48:5)
      at processImmediate (internal/timers.js:456:21)



npm ERR! Test failed.  See above for more details.

Hm, seven failed tests. Let's see if we can get that first test to pass. Open up index.js.

When we write our code, we follow the guidance of the tests. Remember the line, describe('shout(string)', () => { ... }). Well, we know that we need a function called shout that accepts an argument — let's add that first. In index.js:

function shout(string) {
}

And what should that function do? Well, the it() description tells us that it "receives one argument and returns it in all caps".

Okay, so with that information, we know that our function should look like this:

function shout(string) {
  return string
}

But how do we make string all caps? JavaScript has a method for that! It's called toUpperCase(). We can call it on any string:

'Hello!'.toUpperCase() // 'HELLO!'

So let's try it with our shout() function:

function shout(string) {
  return string.toUpperCase()
}

And run our tests again:

learn test
shout(string)
    ✓ receives one argument and returns it in all caps

  whisper(string)
    1) receives one argument and returns it in all lowercase

  logShout(string)
    2) calls console.log() its one argument in all caps

  logWhisper(string)
    3) calls console.log() its one argument in all lowercase

  sayHiToGrandma(string)
    4) returns "I can't hear you!" if `string` is lowercase
    5) returns "YES INDEED!" if `string` is uppercase
    6) returns "I love you, too." if `string` is "I love you, Grandma."`


  1 passing (108ms)
  6 failing

  1) whisper(string)
       receives one argument and returns it in all lowercase:
     ReferenceError: whisper is not defined
      at Context.<anonymous> (test/index-test.js:10:5)
      at processImmediate (internal/timers.js:456:21)

  2) logShout(string)
       calls console.log() its one argument in all caps:
     ReferenceError: logShout is not defined
      at Context.<anonymous> (test/index-test.js:18:5)
      at processImmediate (internal/timers.js:456:21)

  3) logWhisper(string)
       calls console.log() its one argument in all lowercase:
     ReferenceError: logWhisper is not defined
      at Context.<anonymous> (test/index-test.js:30:5)
      at processImmediate (internal/timers.js:456:21)

  4) sayHiToGrandma(string)
       returns "I can't hear you!" if `string` is lowercase:
     ReferenceError: sayHiToGrandma is not defined
      at Context.<anonymous> (test/index-test.js:40:5)
      at processImmediate (internal/timers.js:456:21)

  5) sayHiToGrandma(string)
       returns "YES INDEED!" if `string` is uppercase:
     ReferenceError: sayHiToGrandma is not defined
      at Context.<anonymous> (test/index-test.js:44:5)
      at processImmediate (internal/timers.js:456:21)

  6) sayHiToGrandma(string)
       returns "I love you, too." if `string` is "I love you, Grandma."`:
     ReferenceError: sayHiToGrandma is not defined
      at Context.<anonymous> (test/index-test.js:48:5)
      at processImmediate (internal/timers.js:456:21)



npm ERR! Test failed.  See above for more details.

Hey! We got one to pass! Six left.

Your Turn

Now it's your turn to get the rest of the tests to pass. Note that some of them require you to use console.log() instead of return — follow the guidance of the tests!

In this lab, we're writing functions that "speak" at different volumes — they whisper or they shout. The next test is similar to the first:

1) whisper(string)
       receives one argument and returns it in all lowercase:
     ReferenceError: whisper is not defined
      at Context.<anonymous> (test/index-test.js:10:5)
      at processImmediate (internal/timers.js:456:21)

This test is telling us that whisper(string) received one argument and returns it in all lowercase. At the moment, the test is failing becasue whisper is not defined.

Note: Just like .toUpperCase() changes any string to all uppercase in JavaScript, .toLowerCase() (e.g., 'HELLO'.toLowerCase()) changes any string to all lowercase.

The next two tests are checking to see if a specific string is logged when a function is called. You will still need to use the .toUpperCase() and .toLowerCase() methods for logShout(string) and logWhisper(string). Keep in mind though that these tests are not looking for return values, only logs.

The final function you need to create is sayHiToGrandma(). Grandma is a bit hard of hearing, so whispering can be a bit difficult, but she'll always hear you if you say, "I love you, Grandma." This time, you will need to return different strings depending on the string passed into the function.

Note: Although there are 3 tests for sayHiToGrandma(), you only need to write one function. This function should be able to handle all three test conditions:

  • If the string that is passed into the function is all lowercase, the function should return "I can't hear you!"
  • If the string that is passed into the function is all uppercase, the function should return "YES INDEED!"
  • If the string that is passed into the function is equal to "I love you, Grandma.", the function should return "I love you, too."

How do we check if a string is all lowercase or all uppercase?

var uppercase = "HELLO!"

uppercase.toUpperCase() === uppercase // true

var lowercase = 'hello!'

lowercase.toLowerCase() === lowercase // true

var mixedCase = 'Hi there!'

mixedCase.toLowerCase() === mixedCase // false

mixedCase.toUpperCase() === mixedCase // false

We can simply check whether the string is the same when we convert it to uppercase or lowercase! (The lines with the === comparisons are the ones that check). If it's the same, then it was already in that case; if not, then it's either in the other case or it's mixed case. Now that we know how to compare strings, how can we use these comparisons to conditionally return different strings?

Remember that punctuation is important! Humans might be able to understand that "I love you Grandma" is close enough to "I love you, Grandma." and means the same thing but JavaScript will not consider these equal!

Good luck! When all tests are passing, be sure to run learn submit!

View Intro to Functions Lab on Learn.co and start learning to code for free.