Description

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Beginner · 9 min

Missing values and defaults

Handle null and undefined without replacing valid zero or empty-string values.

Use a nullish default

?? uses its right-hand value only when the left side is null or undefined. It preserves values such as 0, false, and an empty string.

const saved = null;
console.log(saved ?? "Guest");
console.log(0 ?? 10);

Output

Guest
0

Read an optional property

?. stops a property access when the value before it is null or undefined. Combine it with ?? to choose a default.

const user = { name: "Mina" };
console.log(user.address?.city ?? "Not provided");

Output

Not provided

Put it into practice

  1. Predict each result before running the example.
  2. Complete the coding task, then explain why your solution works.

Try it yourself

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Keep a valid zero

Set quantity to savedQuantity unless it is null or undefined. Preserve the saved zero and display quantity.

Practice