Microbit JavaScript
Hard
60 mins
295 points
What you need:
  • Computer/laptop

JavaScript Variables

In this lesson we learn about JavaScript Variables and start coding with them.

1 - JavaScript Variables

Variables are containers for storing data values and objects. For example in a game you might have a 'score' variable. At the start of the game the 'score' variable would be 0 and then each time your get a point in the game it would be added onto the 'score' variable.

Using programming blocks, the code would look like this:

Description Code
Create and set up the score variable.
let score = 0
Add 1 to the score.
input.onButtonPressed(Button.A, function () {
    score += 1
})
Show the score.
basic.forever(function () {
    basic.showNumber(score)
})

Using JavaScript, the code would look like this:

Description Code
Create and set up the score variable.
let score = 0
Add 1 to the score.
input.onButtonPressed(Button.A, function () {
    score = score + 1
})
Show the score.
basic.forever(function () {
    basic.showNumber(score)
})

2 - Adding number variables

In this example apples, oranges and fruit, are variables.

let apples = 4
let oranges = 6
let fruit = apples + oranges

In programming, just like in algebra, we use variables (like apples) to hold values.

In programming, just like in algebra, we use variables in expressions (fruit = apples + oranges).

What value will fruit be equal to?

see the answer

fruit will be equal to 10 (as 4 + 6 = 10).

3 - Adding string variables

In JavaScript we can also "add" or join strings together, this is called concatenating them.

let firstName = "LeBron"
let lastName = "Smith"
let fullName = firstName + " " + lastName // join or concatenate them with a space in the middle

In this example the fullName variable will be equal to LeBron Smith.

4 - JavaScript Identifiers

All JavaScript variables must be identified with unique names. These unique names are called identifiers. Identifiers can be short names (like x and y) or more descriptive names (age, firstName, country).

The general rules for constructing names for variables (unique identifiers) are:

  • Variable names can contain letters, digits, underscores, and dollar signs.
  • Variable names must begin with a letter.
  • Variable names can also begin with $ and _.
  • Variable names are case sensitive (x and X are different variables).

The following are examples of variables named correctly:

let x = 10
let X = 20
let _age = 15
let dateOfBirth = "8/5/2005"
let country_name = "Mexico"
let $height = "5 foot 7 inches"

The following are examples of variables named incorrectly.

let city = "London"
let city = "Dublin"             // can't use the same name
let age% = 15                   // can't use symbols
let date Of Birth = "8/5/2005"  // can't have spaces

5 - Exercise

Now that we've learnt about JavaScript variables, let's create and use some in JavaScript code.

Go to the https://makecode.microbit.org website, create a new project and switch to JavaScript instead of Blocks.

Create the following 3 variables and store your own name and age in them.

  1. firstName
  2. lastName
  3. age

see the code

let firstName = "Evie"  // put in your first name
let lastName = "Molloy" // put in your last name
let age = 12            // put in your age

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