JavaScript Cheatsheet

Variable Declarations

var Declare a variable that can be changed later

let - Declare a variable that can be changed later

const - Declare a variable that can not be changed later

there are some other differences between var and let to do with scope but we won't get into that for now.

Operators

Logical

&& and

|| or

! not

Comparison

== Loose Equal (Equal value)

=== Strict Equal (Equal value && type)

!= Loose Not Equal (Not equal value)

!== Strict Not Equal (Not equal value || type)

> Greater Than

< Less Than

>= Greater Than || Equal To

<= Less Than || Equal To

Arithmetic && assignment

+ Addition

+= Addition assignment

- Subtraction

-= Subtraction assignment

* Multiplication

*= Multiplication assignment

/ Division

/= Division assignment

% Modulus (Returns the remainder of a division)

%= Modulus assignment

** Exponentiation (multiply to the power of)

**= Exponentiation assignment

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Data Types

Primitive Types

1. Number Any number
2. Boolean Represented as True or False (1 or 0)
3. Null Intentional absence of a value (It exists, but it doesn't have a value)
4. Undefined Absense of a value (it doesn't exist)
5. BigInt Used for storing numbers larger than 9,007,199,254,740,991
6. String Grouping of characters, aka text (letters, numbers, spaces, symbols, etc)
7. Symbol Used for anonymouse, unique values. (Useful in complex, security-driven applications)

Conditional Statements

Falsy values

1. 0
2. Empty strings like "" or ''
3. null which represent when there is no value at all
4. undefined which represent when a declared variable lacks a value
5. NaN, or Not a Number

Loops

For

for (param1; param2; param3) {
    // Code block to be executed
}

For loops take in 3 parameters seperated with a semicolin ; instead of the usual comma ,

param1 - executes when the loop starts

param2 - the condition that must be met execute each loop

param3 - executes every time the loop is iterated

Example:

for (let i = 0; i < 10; i++) {
    console.log(i)
}

The above example will log i to the console 10 times as i increases with every iteration

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While

while (condition) {
    // Code block to be executed
}

While loops take in a condition and will loop until that condition is no longer true

*Be extremely careful with while loops, as they are extremely easy to get stuck in an infinite loop, this can crash the page and/or computer running it.

Example

let i = 0 // If we left out this line, it would never run!
while (i < 10) {
    console.log(i)
    i++ // If we forgot this, it would loop infinitely
}

The above example will run 10 times, as you can see, we need to declare the value of i outside the loop. Otherwise it would never start the loop, because JavaScript doesn't know what i means

If we were to forget to increment i after each iteration, it would run forever. Since the condition would never be false, as i would never get higher than 0