JavaScript JSON

JSON (JavaScript Object Notation) is a text format to store and send data. It looks like a JavaScript object. Almost every web API uses it.

{
  "name": "Robin",
  "age": 25,
  "skills": ["HTML", "CSS"],
  "active": true
}

---

Rules of JSON

• Keys must be in double quotes.
• Strings use double quotes only, not single quotes.
• Values can be string, number, boolean, null, array or object. No functions, no undefined, no comments.
• No trailing comma after the last item.

---

JSON.stringify: object to text

const user = { name: "Robin", age: 25, skills: ["HTML", "CSS"] };

const text = JSON.stringify(user);
console.log(text);
console.log(typeof text);

Use JSON.stringify(obj, null, 2) to get nicely indented text for reading.

---

JSON.parse: text to object

const json = '{"name":"Maria","age":30}';
const obj = JSON.parse(json);

console.log(obj.name);
console.log(obj.age + 1);

---

Handle wrong JSON

JSON.parse() throws an error if the text is not valid JSON, so wrap it in try...catch (see Error Handling).

try {
  JSON.parse("{name: 'Robin'}");   // keys without quotes: invalid
} catch (e) {
  console.log(e.name);
}

---

Copy an object with JSON

const original = { a: 1, list: [1, 2] };
const copy = JSON.parse(JSON.stringify(original));
copy.list.push(3);
console.log(original.list);

This makes a deep copy, but it loses functions, undefined and dates. The newer structuredClone() is a better choice.

---

Summary

• JSON is text. Keys and strings need double quotes.
• JSON.stringify() turns an object into JSON text, JSON.parse() does the reverse.
• Always use try...catch with JSON.parse().
• Next: JavaScript Date.

• Previous Page
• Next Page

---

Exercises & Assignments
No Content Found.

Interview Questions & Answers
No Content Found.