JS: Optional Chaining Operator

(new in ECMAScript 2020)

obj?.prop

Return the property value of object obj if it exist, but if obj is undefined or null or prop does not exist, return undefined.

🟢 TIP: This is useful when you have a long chain such as a.b.c.d , and some property may not exist. With the normal dot notation, it would error out.

const xx = {};
// access a property that does not exist.
// does not result in error.
console.assert(xx?.aa === undefined);

const xx = { a: { b: 3 }, c: 2 };

// success
console.assert(xx?.a?.b === 3);

// property yy no exist, but do not generate error.
console.assert(xx?.yy?.b === undefined);

// test the behavior of Optional Chaining Operator
console.assert(undefined?.x === undefined);
console.assert(null?.x === undefined);