(??)

const foo = null ?? "default string";
console.log(foo);
// Expected output: "default string"

const baz = 0 ?? 42;
console.log(baz);
// Expected output: 0

leftExpr ?? rightExpr;

const nullValue = null;
const emptyText = ""; // 
const someNumber = 42;

const valA = nullValue ?? "  A";
const valB = emptyText ?? "  B";
const valC = someNumber ?? 0;

console.log(valA); // "  A"
console.log(valB); // "" (      null  undefined)
console.log(valC); // 42

let foo;

// foo     ,   undefined
let someDummyText = foo || "Hello!";

let count = 0;
let text = "";

let qty = count || 42;
let message = text || "hi!";
console.log(qty); // 42,   0
console.log(message); // "hi!",   ""

let myText = ""; //   ( )

let notFalsyText = myText || ", ";
console.log(notFalsyText); // , 

let preservingFalsy = myText ?? ", ";
console.log(preservingFalsy); // '' (.. myText   undefined,  null)

function A() {
  console.log(" A");
  return undefined;
}
function B() {
  console.log(" B");
  return false;
}
function C() {
  console.log(" C");
  return "foo";
}

console.log(A() ?? C());
//      " A",  " C",   "foo",
// .. A()  undefined,     

console.log(B() ?? C());
//     " B",  "false",
//  B()  false ( null  undefined), 
//    

null || undefined ?? "foo"; //  SyntaxError
true || undefined ?? "foo"; //  SyntaxError

(null || undefined) ?? "foo"; //  "foo"

let foo = { someFooProp: "" };

console.log(foo.someFooProp?.toUpperCase() ?? " "); // ""
console.log(foo.someBarProp?.toUpperCase() ?? " "); // " "