Property access
- Node.js course
- Beginner
- Lesson 66/116
- 5 min
Learn to access properties with . and [].
Property access
There are two ways to access an object's property: the dot and the bracket. Both give the same result, but they fit different situations.
Dot notation: user.name. When the property name is a valid identifier (letters, digits, underscore; not starting with a digit) the dot is preferred. It is shorter and clearer.
Bracket notation: user['name']. When the name contains spaces or hyphens, or is computed at runtime, brackets are required. Example: user['full name'] cannot be written with a dot.
Dot or bracket?
When choosing between dot and bracket, look at the structure of the property name. If it is a valid identifier and known up front, the dot is best. If the name comes from a variable, contains spaces, or uses special characters like hyphens, you must use brackets.
Dynamic access example: const key = 'age'; console.log(user[key]). Here key carries the name, so brackets are required; writing user.key would look for a property literally named 'key' and return undefined.
Accessing a missing property returns undefined in both notations; no error is thrown. So to check existence you can use user.name !== undefined or 'name' in user.
Practice Print a product's price
Define a product object as { name: 'Kalem', price: 25, stock: 100 }. Access the price property with brackets (product['price']) and print it with console.log.
Starter code
// Define the product object, print price using bracketsSample solution
const product = { name: 'Kalem', price: 25, stock: 100 };
console.log(product['price']);Expected output
25
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Access with brackets
const user = { name: 'Ayşe', age: 30 };
console.log(user[____]);const user = { name: 'Ayşe', age: 30 };
console.log(user['name']);Explanation: user['name'] is the bracket access.
2 When are brackets required?
- When the name is short
- When the name has a space Correct answer
- When the object is large
- When the value is numeric
Explanation: names with spaces cannot use the dot.
3 Match the access forms
| Term | Meaning |
|---|---|
user.name |
Dot access |
user['name'] |
Bracket access |
user[key] |
Dynamic access |
undefined |
Result of a missing property |