JSON.parse() Reviver

JSON Reviver

The reviver function in JSON.parse() transforms values during parsing. Use it to revive Date strings into Date objects.

Example

const json = '{"name":"Alice","createdAt":"2024-06-15T10:30:00.000Z"}';

// Without reviver: createdAt is a plain string
const raw = JSON.parse(json);
console.log(raw.createdAt instanceof Date); // false

// With reviver: convert ISO strings to Date objects
const parsed = JSON.parse(json, (key, value) => {
  if (typeof value === "string" && /^\d{4}-\d{2}-\d{2}T/.test(value)) {
    return new Date(value);
  }
  return value;
});
console.log(parsed.createdAt instanceof Date); // true

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Pro Tip

Use a reviver to restore Date objects from JSON — they serialize to strings and lose their Date type otherwise.

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