What is an Operator?

An OPERATOR is a SYMBOL that represent an OPERATION to be taken on one or more VALUES

Operators can be represented by one or more characters.

e.g. +, -, *, ||, &&

Types of Operators

• Unary Operators

  • One operator with one value

• Binary Operators

  • One operator with two values
  • Arithmetic Operators
  • Logical Operators
  • Comparison Operators
  • Assignment Operators

• Trinary Operators

  • One operator with three values
  • The Ternary Operator

The Unary +

The + operator can be used on a single value to convert that value into a number.

+'33'     // => 33
+'0'      // => 0
+''       // => 0
+' '      // => 0
+'cheese' // => NaN

typeof

typeof is a unary operator that returns the type of the operand

typeof function() {...}   // => 'function'
typeof "Hello, world!"    // => 'string'
typeof [1, 2, 3, "red"]   // => 'object'
typeof unassignedVariable // => 'undefined'
typeof false              // => 'boolean'
typeof null               // => 'object'

Increment and Decrement

Increment and decrement change their variable operand.

• ++ increment the variable by one
• -- decrement the variable by one

let myNumber = 3;

myNumber++
console.log(myNumber); // => 4

myNumber--
console.log(myNumber); // => 3

"cheese"++             // => NaN

NOTE: Increment and decrement only work on variables which have a Number value.

Arithmetic Operators

Accept two number values and perform an operation on them.

Returns a NEW number as a result.

• + Addition
• - Subtraction
• * Multiplication
• / Division
• % Modulus
• ** Exponent

2 + 1  // => 3
2 - 1  // => 1
2 * 2  // => 4
6 / 2  // => 3
6 % 3  // => 0
5 ** 2 // => 25

Lab: Arithmetic

Open a terminal and start node, or create a new JavaScript file.

Determine answers to the following questions using arithmetic operators.

• Does JavaScript follow order of operations when parsing equations?
• What happens when you try to add a string number (e.g. "12") to a number?
• What happens when you try and subtract a string number from a number?
• What happens when you perform arithmetic operations on strings?
  • Addition?
  • Subtraction?
  • Multiplication?
  • Division?
• Can you perform operations on NaN?

Logical Operators

Evaluate two expressions and return a boolean

• && and; returns true if BOTH sides are considered truthy
• || or; returns true if EITHER side is considered truthy
• ! not; inverts the result of the preceding expression

'dog' && 'cat'     // => 'cat'
null && 'cat'      // => false
'dog' || 'cat'     // => 'dog'
undefined || 'cat' // => 'cat'
!true              // => false
!(7 < 5)           // => true

Comparison Operators

Compare two values and returns a boolean

• > greater than
• < less than
• >= greater than or equal to
• <= less than or equal to

5 > 3 // => true
5 < 3 // => false
5 >= 3 // => true
5 <= 5 // => true

Equality Operators

• == equal to
• === identical
• != not equal
• !== not identical

5 == '5'        // => true
true == '1'     // => true

5 === '5'       // => false
true === '1'    // => false

'cat' != 'dog'  // => true
'cat' !== 'cat' // => false

Equals vs. Identity

There is a difference between the double equals == and triple equals ===.

The double equals will try and coerce the operands so that are comparable.

The triple equals will only perform a comparison on the values as they are.

When comparing two values you should always use the triple equals.

Lab: Compare and Contrast

Open up a node environment in your terminal, and let's play around with some comparison operators.

• What happens when you compare two strings with greater than >?
  • Did it result in the value you expected?
  • How are they being compared?
• Find a difference between the double equals == and triple equals ===

Assignment Operators

Modify an existing value by some other value.

• = sets the variable on the left equal to the value on the right
• += adds the value to the right to the variable on the left
• -= subtracts the value to the right from the variable on the left

let x = 7
let y = 3

x += 1 // x => 8
y += 3 // y => 6

x += y // x => 14
y -= x // x => -8

Lab: Assignment

Open a terminal and start node, or create a new JavaScript file.

• Assign a variable x using the let keyword to a numerical value.
• Assign a variable y using the const keyword to a numerical value.
• Add a value to x using the += operator. What's the value of x?
• Add a value to y using the += operator. Did you get the value you expected?
• Create a variable named string that is a string.
  • Add a value to string using +=, what is the value of string?
  • What is the value of string if you use -= instead?

The Ternary Operator

The ternary operator is the only trinary operator in JavaScript

expression ? valueOne : valueTwo 
// If the expression evaluates to true returns valueOne
//   otherwise returns valueTwo

let isAllowed = true;

return isAllowed ? 'You are allowed' : 'You are denied';
// => 'You are allowed'