JavaScript for Beginners

Class 2

You Will Learn About:

• Variables
• Math Operators
• Strings
• Functions
• Arguments
• Return Values

Variables

A variable is a place to store values

Variable Values

• When you first create a variable, it does not have a value (it is undefined).
• You can set a value for a variable.
• Variables can hold different types of information, like words, numbers, and collections of data.
• The value of a variable can change over time.

Naming Variables

• The variable name is case-sensitive.
• A new variable needs to have a unique name.
• Variable names need to start with a letter, $, or _.
• Variable names can only be made of letters, numbers, $, or _.

Declaring a Variable

To declare (create) a variable, just type the word "var" and the variable name.

<script>
  var numberOfKittens;
</script>

It is a good idea to give your variable a starting value. This is called initializing the variable.

<script>
  var numberOfKittens = 5;
</script>
						

Using a Variable

Once you have created a variable, you can use it in your code. Just type the name of the variable.

<script>
  var numberOfKittens = 5;
  console.log (numberOfKittens);
</script>
						

Let's Develop It

In your JS file, create a variable and give it a valid name and a value. Then, display the value.

Numbers

Variables can be numbers, either integers or floats (decimals).

<script>
  var numberOfKittens = 5;
  var cutenessRating = 9.6;
</script>
						

The browser will automatically convert integers to floats if needed

Arithmetic Operators

Once you have numbers, you can do math with them!

<script>
  var numberOfKittens = 5;
  var numberOfPuppies = 4;
  var numberOfAnimals = numberOfKittens + numberOfPuppies;
</script>
						

Arithmetic Operators

Let's Develop It

Create two variables and try some arithmetic operators. Don't forget to display your results!

Strings

Variables can be strings, groups of characters. You put your string in quotes.

<script>
  var kittensName = 'Fluffy';
</script>
						

If you want to use a quote in your string, you'll need to "escape" it with a backslash.

<script>
  console.log('I\'d like to use an apostrophe');
</script>
						

String Operators

You can put strings together with a +, the concatenation operator.

<script>
  var kittensName = 'Fluffy ';
  var fullName = kittensName + ' McDougle';
  console.log(fullName); //Outputs 'Fluffy McDougle'
</script>
						

String Operators

You can also use += to add things to the end of a string.

<script>
  var kittensName = 'Admiral ';
  kittensName += ' Snuggles';
  console.log(kittensName); //Outputs 'Admiral Snuggles'
</script>
						

Let's Develop It

Create two variables, a first name and a last name, and then put them together to make a full name. Don't forget to display your results!

Functions

Functions are separable, reusable pieces of code.

Using Functions

First, declare the function.

<script>
  function turtleFact() {
    console.log('A turtle\'s lower shell is called a plastron.');
  }
</script>
						

Then, use it as many times as you want!

<script>
  turtleFact();
</script>
						

Arguments

Functions can accept input values, called arguments.

<script>
  function callKitten (kittenName){
    console.log('Come here, ' + kittenName + '!');
  }
  callKitten ('Fluffy'); //outputs 'Come here, Fluffy!'

  function addNumbers(a, b) {
    console.log(a + b);
  }
  addNumbers(5,7); //outputs 12
  addNumbers(9,12); //outputs 21
</script>
						

Arguments

You can also pass variables into functions. These variables do not need to have the same name as the function arguments.

<script>
  function addOne(inputNumber){
    var newNumber = inputNumber + 1;
    console.log('<p>You now have ' + newNumber);
  }
  //Declare variables
  var numberOfKittens = 5;
  var numberOfPuppies = 4;
  //Use them in functions
  addOne(numberOfKittens);
  addOne(numberOfPuppies);
</script>
						

Let's Develop It

Turn the code you wrote to output someone's full name into a function, then use it.

Returning Values

You can have a function give you back a value.

<script>
  function addNumbers(num1, num2){
    return num1 + num2;
  }

  var resultOfAddingNumbers = addNumbers(2,2);
  console.log(resultOfAddingNumbers);

  function subtractNumbers(num1, num2){
    num1 - num2;
  }

  var resultOfSubtractingNumbers = subtractNumbers(2,2);
  console.log(resultOfSubtractingNumbers);

</script>
						

Return will immediately end a function.

Let's Develop It

Add a return statement to your name function. Use that function to set the value of a variable.

Summary

• Variables
• Math Operators
• Strings
• Functions
• Arguments
• Return Values

Resources

• JavaScript Guide, from the Mozilla Developers Network.
• Codecademy, with interactive JavaScript lessons to help you review.