//nullish coalescing operator in js

Expression:

    Left ?? Right

if left is null or undefined , then Right will be the value

​

let value = null ?? "Oops.. null or undefined";

console.log(value) //Oops.. null or undefined

​

value = undefined ?? "Oops.. null or undefined";

console.log(value) //Oops.. null or undefined

​

value = 25 ?? "Oops.. null or undefined";

console.log(value) // 25

​

value = "" ?? "Oops.. null or undefined";

console.log(value) // ""

The nullish coalescing operator ( ?? ) is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined , and otherwise returns its left-hand side operand

// The nullish coalescing operator (??) provides a concise way to 

// assign a default value to a variable if the variable is null or undefined.

// (??) considers values that are not null or undefined as truthy. 

const res1 = undefined ?? 'Default'; // res7: 'Default'

const res2 = null ?? 'Default'; // res1: 'Default'

const res3 = NaN ?? 'Default';  // res3: 'Default'

const res4 = false ?? 'Default';// res5: false

const res5 = true ?? 'Default'; // res7: true

const res6 = '' ?? 'Default';   // res2: ''

const res7 = {} ?? 'Default';   // res6: {}

const res8 = 0 ?? 'Default';    // res4: 0

​

The OR operator || uses the right value if left is falsy 

(e.g. "" or 0 or false), while the nullish coalescing operator ?? uses

the right value if left is null or undefined.

/* The coalescing operator is very nice to use with the optional chaining

for setting a default value. Thus, you could use the code below to fall

back on a default phone number which is an empty string */

​

const contactInfos = { address: "20B Rue Lafayette" };

console.warn(contactInfos.user?.phoneNumber ?? "")

// ""

const value = null ?? 'Default Value';

console.log(value);  // Output: 'Default Value'

const defaultValue = 'Default Value';

const value1 = null;

const value2 = undefined;

const value3 = 'Actual Value';

​

console.log(value1 ?? defaultValue); // Output: Default Value

console.log(value2 ?? defaultValue); // Output: Default Value

console.log(value3 ?? defaultValue); // Output: Actual Value