Read Values from JSON and JavaScript Objects

“Reading a JSON value” usually involves two operations: parse a JSON string into a JavaScript object, then access properties on that object.

const text = '{"name":"Tom","age":18}';
const user = JSON.parse(text);

console.log(user.name);
console.log(user["age"]);

Use dot notation for fixed identifier-like names. Use brackets for dynamic or special names:

const key = "name";
console.log(user[key]);

const config = {
  "user-name": "Tom",
  "display name": "Tom Cat"
};
console.log(config["user-name"]);

Dynamic keys can be assembled normally:

for (let i = 1; i <= 3; i++) {
  console.log(data[`r${i}`]);
}

Iterate with Object.keys, Object.values, or Object.entries:

for (const [key, value] of Object.entries(data)) {
  console.log(key, value);
}

Use optional chaining when intermediate properties may be absent:

const name = result.user?.profile?.name ?? "Not set";

Only strings need JSON.parse. Many HTTP libraries already return parsed objects, and parsing them again causes an error.