Generating JSON in JavaScript

JSON.stringify() does the reverse of parsing — it converts a JavaScript object or array into a JSON-formatted text string, ready to send over a network or save to a file.

JSON.stringify()

Passing a JavaScript object to JSON.stringify() produces a compact JSON string. Optional second and third arguments let you filter which properties are included and add indentation for readability.

const user = { name: "Naledi", age: 24, password: "secret123" };

const jsonString = JSON.stringify(user);
console.log(jsonString); // {"name":"Naledi","age":24,"password":"secret123"}

const pretty = JSON.stringify(user, null, 2); // indented with 2 spaces
console.log(pretty);

const filtered = JSON.stringify(user, ["name", "age"]); // exclude password
console.log(filtered); // {"name":"Naledi","age":24}

Common Mistakes

• Forgetting that JSON.stringify() silently drops functions, undefined values, and Symbol properties from the output.
• Accidentally including sensitive fields (like a password) in stringified data sent to a client or logged somewhere insecure.
• Assuming JSON.stringify() preserves the exact key order guaranteed in all cases — while modern engines generally preserve insertion order for string keys, it's not something to rely on for critical logic.
• Not using the indentation argument when generating JSON meant to be human-readable, like a config file.