Stage 1 · Lesson 6 of 9
null, undefined and optional values
has two empty values. undefined is what you get for a missing property or a variable with nothing in it yet. null is usually set on purpose.
With strict mode, a string cannot hold either unless its type says string | undefined, so the compiler makes you handle the gap. Use to read safely, as in user?.profile?.photo, and nullish coalescing, ??, for a default.
Know why ?? is safer than ||. count || 10 turns a real 0 into 10, while count ?? 10 keeps it.
Common trapthe non-null assertion user!.name, which tells the compiler to trust you and crashes at runtime when the data is missing.
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Resources for this stage
Start with· follow one of these
- CoursePaidGrokking JavaScript Fundamentals
Design Gurus · Beginner · $50
Beginner JavaScript with an exercise after most lessons
- GuideFreeJavaScript.info
Ilya Kantor
Free and thorough: Part 1 is the language, skip the browser chapters in Part 2