Logical / JavaScript Operator

# Web Site Writing Basics

# javascrip

# The logical operator

Logical Operators in JavaScript use Boolean: true or false) or to control the operation of conditions. They work on a principle called Short-Circuit Evaluation. This means that they may stop evaluating the remaining Operand as soon as the final result is known.

There are 3 main operators:

1. (OR: OR)

The OR operator is used to determine if a condition is true.

Truth table: It returns true if one or both operands are true.

Short-Circuit Operation:

It will evaluate the operand from left to right.

As soon as the first operand is found to be Truthy (considered true), it restores the value of that operand and stops evaluating.

If all operands were Falsy (considered false), it would restore the value of the last operand.

Example Results Reason

'True false. '

'0 5 '

'"null'

General benefit: Used to define Default Value if the first value is null or undefined.

JavaScript

let userName = userSetting | | 'Guest';

/ / If userSetting is null / undefined / "/ 0, userName is set to 'Guest'.

2. & & (AND: AND)

The AND operator is used to determine if all conditions are true.

Truth table: It returns true only if both sides of the operand are true.

Short-Circuit Operation:

It will evaluate the operand from left to right.

As soon as the first operand is found to be Falsy (considered false), it restores the value of that operand and stops evaluating.

If all operands were Truthy, it would restore the value of the last one.

Example Results Reason

The first true & & false false is true, but the second is false, thus restoring false (the second).

5 & & "Hello" "Hello" Both Are Truthy Restore Last

0 & & "World" 0 0 is Falsy immediately returns 0.

Typical Benefits: Used to Make Conditional Rendering or Call Conditional Functions (Used instead of Short If Structures)

JavaScript

/ / If isLogged is true, call the showProfile function.

isLogged & showProfile ();

3.! (NOT: NOT)

The NOT operator is used to reverse the logical value.

Operation: It will convert the operand into a logical value (Boolean) and then reverse it.

! True, false.

! False is true.

Example Results Reason

! True, false. Back up.

! 0 true 0 to Falsy was converted to false and then returned to true.

! "Hello" is true! The first converts "Hello" (Truthy) to false and the second back to true.

Export to sheet

General benefit: Used to verify whether a value is Falsy or Truthy (using!! to convert any value into an authentic Boolean).

Falsy and Truthy Values in JavaScript

In JavaScript logic valuation, the following values are assumed to be Falsy (equivalent to false):

False

0 (zero)

"" (empty string)

Null

Undefined

NaN (Not-a-Number)

Truthy is all other values that are not in the Falsy list (e.g. 1, "hello," [], {}).