Numbers

• Made of the digits 0…9

• No quotes

Strings

• Made of any characters

• Inside double quotes

Operators

• Fancy name for +-*/

Expression

• Combination of operators and values

• Evaluates to a single value

Variables

• Can hold at most 1 value

• Name uses no quotes, includes no spaces, and must start with a letter

• A reference to a value or expression that can be used repeatedly throughout a program

var

• Creates a new variable

Numbers and strings are 2 different types of values

Expressions evaluate to a single new value

When variables are in the expression just make a copy, don’t change the actual variable

Variables are “assigned” a new value

Evaluate first, then assign

Old values are deleted forever

Assignment just moves information around. It does not “connect” variables

In Javascript, the assignment operator is written as “=”

Assignment Operator

• Allows a program to change the value represented by a variable

Counter Pattern with Event

Variable with String Concatenation

Debugging: the process of finding and fixing problems in code

• Describe the problem

  • What do you expect it to do?

  • What does it actually do?

  • Does it always happen?

• Hunt for bugs

  • Are there warnings or errors?

  • What did you change most recently?

  • Explain you code to someone else

  • Look for code related to the problem

• Try solutions

  • Make a small change

• Document as you go

  • What have you learned?

  • What strategies did you use?

  • What questions do you have?

• Slow down code with the speed slider

• Use console.log to get output

• Use Watchers to see your variables change values

• Syntax Error

  • Your code doesn’t follow the rules of the programming language

    • Writing a variable name in quotes

    • Using a variable that doesn’t exist

  • Check warnings and errors

• Logic Error

  • Your code follows the rules of the programming language but doesn’t do what you intend

    • Writing if-else-if statements in the wrong order

    • Updating the property of the wrong element

  • Test your code

Create Variables Once, At the Top, Outside Functions or onEvent()

• Use var only once. You don’t need to create variables twice, and this can cause errors

• Create your variables at the top of your program. This keeps you code organized and easier to read for you and others

• Create your variables outside any function or onEvent() blocks

Global vs. Local Variables

• There’s 2 types of variables, global and local, and so far we’ve only used global variables

• Global

  • Permanent. Can be used anywhere in your code

  • var used outside an onEvent()

• Local

  • Temporary. Can be used only in the part of the code where it was created, like inside an onEvent(). Deleted once the onEvent() is done running

  • var used inside an onEvent()

• Make sure that you’re not using var inside of an onEvent() or function

Boolean value

• A data type that is either true or false

Boolean Expression

• Evaluates to either true or false

Comparison operators

• Indicate a Boolean expression

• < less than

• greater than

• == equal to

• <= less than or equal to

• = greater than or equal to

• != not equal to

Logical operators

• Boolean values are a type of information, so they can be evaluated in a Boolean expression using logical operators

• Both sides of the logical operator are reduced to a single Boolean value

• && and

  • Both must be true for the Boolean expression to evaluate as true

• || or

  • Either may be true for the Boolean expression to evaluate as true

• != not

  • Opposite of the Boolean value

  • Not true: flase

  • Not false: true

• If something is true and (&&) false, it evaluates to false

Single values are compared and result in a Boolean value (true or false)

A truth table is is used to evaluate the reduced Boolean expression to a single Boolean value

A decision is made with the single Boolean value

A flowchart illustrates the steps of making a decision with a Boolean expression

“when”

• Means there is an onEvent to respond to user input. The app does something “when” the user clicks

“if”

• Means there is a conditional statement that decides what pieces of code to run. The app does something “if” a boolean expression evaluates to true

MOD

• The remainder that is left after a number is divided by another number

• A common usage is to determine if a number is even or odd. If you divide any number by 2 and there is no remainder, the number is even

• You can use MOD to determine if a number is divisible by another number

Checking Multiple Conditions with If-Else-If

The updateScreen() Pattern

Function

• A named group of programming instructions. Also referred to as a “procedure”

Function call

• A command that executes the code within a function