Summary - Boolean logic

JavaScript course · Beginner · Lesson 93/133

Write a safe user profile fetcher using short-circuit, nullish and optional chaining.

Summary - Boolean logic

In this group you learned all the tools of boolean logic. You started with boolean values (true/false) and comparisons. You saw that short-circuit makes && and || return values.

Then you learned nullish coalescing (??) for null/undefined defaults, optional chaining (?.) for safe access, and logical assignment (&&=, ||=, ??=) for short updates. Now you will combine them in a user profile function.

Exercise Safe user profile

Define a function called getUserCity. It takes a user parameter. Inside, write const city = user?.address?.city ?? "Unknown" and return it with return city.

Show example solution

function getUserCity(user) {
  const city = user?.address?.city ?? "Unknown";
  return city;
}

Exercise Safely update preferences

Set prefs to { lang: null, notifications: 0 }. Write prefs.lang ??= "en". Write prefs.notifications ||= 5. Print prefs.

Show example solution

const prefs = { lang: null, notifications: 0 };
prefs.lang ??= "en";
prefs.notifications ||= 5;
console.log(prefs);

Test yourself

Match operator to purpose

?.

safe access
??

null/undefined default
||=

assigns when falsy
&&

guard

Safe access operator

const user = null;
const name = user____.name ?? "Anonymous";
console.log(name);

Show answer

const user = null;
const name = user?..name ?? "Anonymous";
console.log(name);

All lessons in Beginner

1 Variables and data types

Summary - Boolean logic