Summary of uncommon operators and operators in js

Summary of common operators and operators in javascript

Uncommon operators and operators in js

Nullish coalescing operator: ??

When the left operand is null or undefined, it returns the right operand, otherwise it returns the left operand.

null ?? 'huli' // huli
undefined ?? 'huli' // undefined
'' ?? 'huli' // ''
[] ?? 'huli' // []
({}) ?? 'huli' // {}
NaN ?? 'huli' // NaN
false ?? 'huli' // false
0 ?? 'huli' // 0

Logical null assignment: ??=

The logical null assignment operator (x ??= y) assigns a value to x only if it is nullish (null or undefined).

const a = { duration: 50 };

a.duration ??= 10;
console.log(a.duration);
// expected output: 50

a.speed ??= 25;
console.log(a.speed);
// expected output: 25

Logical OR: ||

If the existence is true, then it is true, , whichever is the previous

const a = 3;
const b = -2;
console.log(a > 0 || b > 0); // true

Can be a false value

null
undefined
NaN
"" and''
0
false

Logical or assignment: ||=

If yes, return; if no, assign value

const a = { duration: 50, title: '' };

a.duration ||= 10;
console.log(a.duration);
// expected output: 50

a.title ||= 'title is empty.';
console.log(a.title);
// expected output: "title is empty"

Logical AND: &&

If both exist, it is true, whichever is the latter.

const a = 3;
const b = -2;

console.log(a > 0 && b > 0);
// expected output: false

Logical AND assignment: &&=

Assign if exists

let a = 1;
let b = 0;

a &&= 2;
console.log(a);
// expected output: 2

b &&= 2;
console.log(b);
// expected output: 0

Optional chaining operator: ?.

The optional chaining operator ( ?. ) allows reading the value of a property that is deep in a chain of connected objects without having to explicitly verify that each reference in the chain is valid. The ?. operator functions similarly to the . chaining operator, except that instead of causing an error if the reference is nullish (null or undefined), the expression short-circuits to return undefined. When used with a function call, if the given function does not exist, undefined is returned.

const adventurer = {
  name: 'Alice',
  cat: {
    name: 'Dinah'
  }
};

const dogName = adventurer.dog?.name;
console.log(dogName);
// expected output: undefined

console.log(adventurer.someNonExistentMethod?.());
// expected output: undefined

Summarize

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