Logical Operators

JavaScript Logical Operators

|| (OR) - First Truthy Value

Returns the first truthy value it finds, or the last value if all are falsy:

const result = false || null || "hello" || "world";
console.log(result); // "hello" (first truthy)

const result2 = false || null || undefined;
console.log(result2); // undefined (last value)

&& (AND) - First Falsy Value

Returns the first falsy value it finds, or the last value if all are truthy:

const result = "hello" && "world" && 42;
console.log(result); // 42 (all truthy, returns last)

const result2 = "hello" && false && "world";
console.log(result2); // false (first falsy)

?? (Nullish Coalescing) - Only for null/undefined

Returns the right side only if left side is null or undefined:

const result = null ?? "default";      // "default"
const result2 = undefined ?? "backup"; // "backup"
const result3 = 0 ?? "fallback";       // 0 (not null/undefined!)
const result4 = "" ?? "empty";         // "" (not null/undefined!)

?: (Ternary) - Conditional Expression

Short if/else statement:

const age = 20;
const status = age >= 18 ? "adult" : "minor";
console.log(status); // "adult"

Comparison Table

Operator	Behavior	Use Case	Example
||	First truthy or last value	Default for any falsy	name \|\| "Guest"
&&	First falsy or last value	Conditional execution	user && user.greet()
??	Right side if left is null/undefined	Default for null only	count ?? 0
?:	True/false branching	Conditional assignment	age >= 18 ? "adult" : "minor"

Practical Examples

Default Values

// Using || (falsy fallback)
const name1 = user.name || "Guest";     // Falls back for "", 0, false, null, undefined

// Using ?? (null/undefined only)  
const name2 = user.name ?? "Guest";     // Only falls back for null, undefined

Short-circuit Evaluation

// && for conditional execution
user && user.greet();        // Only call if user exists

// || for default assignment
this.data = this.data || []; // Set to empty array if falsy

Key Point: The ?? is super useful when 0, "", or false are valid values you want to keep!

---

function lol({name,age}={}){
  console.log(name)
  console.log(age)
}
user={
  name:"ll",
  age:25,
  mail:"notuseful",
  idk:"what will hppn"
}
lol(user)