Object keys and values in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are object keys in JavaScript?

Object keys are the names or identifiers used to access values stored in an object. They are always strings or symbols.

beginner

How do you get all keys of an object in JavaScript?

You use Object.keys(yourObject) to get an array of all keys in the object.

beginner

What does Object.values(obj) return?

It returns an array containing all the values of the object's own enumerable properties.

intermediate

Can object keys be numbers in JavaScript?

No, object keys are always strings or symbols. If you use a number, JavaScript converts it to a string.

intermediate

How can you loop through all keys and values of an object?

You can use a for...in loop to go through keys, then access values with obj[key]. Or use Object.entries(obj) to get key-value pairs.

Which method returns an array of an object's keys?

A Object.values()

B Object.keys()

C Object.entries()

D Object.getOwnPropertyNames()

Object.keys() returns an array of the object's own enumerable property names (keys).

What type are object keys in JavaScript?

A Only numbers

B Any data type

C Booleans

D Strings or symbols

Object keys are always strings or symbols. Numbers are converted to strings.

What does Object.values(obj) return?

A An array of values

B An array of keys

C An array of key-value pairs

D The object itself

Object.values(obj) returns an array of the object's own enumerable property values.

How can you get both keys and values together from an object?

A Object.entries()

B Object.values()

C Object.keys()

D Object.getOwnPropertyDescriptors()

Object.entries() returns an array of [key, value] pairs from the object.

What happens if you use a number as an object key?

A It stays a number key

B It causes an error

C It becomes a string key

D It becomes a boolean key

JavaScript converts number keys to strings automatically.

Explain how to retrieve all keys and values from a JavaScript object.

Think about methods that return arrays representing keys, values, or both.

Describe what types object keys can be and what happens if you use a number as a key.

Consider how JavaScript treats keys internally.