Node.js
Property access
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.
Exercise 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.
Show example solution
const product = { name: 'Kalem', price: 25, stock: 100 };
console.log(product['price']);
Test yourself
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Access with brackets
const user = { name: 'Ayşe', age: 30 };
console.log(user[____]);
Show answer
const user = { name: 'Ayşe', age: 30 };
console.log(user['name']);
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When are brackets required?
- When the name is short
- When the name has a space
- When the object is large
- When the value is numeric
Show answer
When the name has a space — names with spaces cannot use the dot.
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Match the access forms
- user.name
- Dot access
- user['name']
- Bracket access
- user[key]
- Dynamic access
- undefined
- Result of a missing property
Next lesson: Computed properties
