JSON vs Object.

Storage chapter. An app is more useful when it remembers data. But browser memory (and files, and the network) holds only TEXT — so first you must tell JSON from a JS object.

Theory. A JS object is a live value in memory: it has properties and you can change it. JSON is text in a strict format: keys in double quotes, no functions, no undefined, no comments. JSON.stringify(object) turns an object into such text; JSON.parse(text) turns it back.

Small examples:

const obj = { name: "Rent", amount: 500 }; const text = JSON.stringify(obj); typeof obj; // "object" typeof text; // "string" text.length; // length of the text, not a property count

JSON text is a plain string — you can save it, but text.amount is undefined.

Common mistake: thinking JSON is an object; reading a property from a JSON string; expecting functions and Date to survive.