Objects – Methods (keys, values, entries)

Returns an array containing all the keys of a given object.

Part of: JavaScript Coding without HTML and CSS — Module 33

Understanding Objects – Methods (keys, values, entries) in JavaScript

What it does: Object.entries() gives back an array of [key, value] pairs. keys() returns just the names of the object's properties. Object.keys() collects every key from the object into an array. JavaScript requires a capital O: Object.keys(). Object.keys(), values(), and entries() all need an object to inspect. The method name must be lowercase: keys(). JavaScript's built-in is Object, not object.

Common mistakes: 'Object' must start with a capital O, not lowercase. 'keys' must be lowercase - a capital K causes an error.

Class: _____________________ · Name: _____________________ · Date: _________

Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 31–40) and word search (Modules 21–52).

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Each concept is reinforced from every angle — learned, then applied, then tested.

Learning

Duo

Does Object.keys() return an array of an object's keys?

YesNo

Matches

console.log(object.keys(a));

↓

Wrong - 'Object' must start with a capital O

Applying

Meanings

Term

Object.keys()

Meaning

Returns an array containing all the keys of a given object.

Practice

let person = {name: "Sam", age: 12};

Testing

Gaps

console.log(Object.(person));

Check Answer

Spots

1console.log(object.keys(a));

2let a = {x: 1};

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Quick Questions

1. Does Object.keys() return an array of an object's keys?

A. No

B. Yes ✓

Object.keys() collects every key from the object into an array.

2. Does Object.values() return an array of an object's values?

A. No

B. Yes ✓

Object.values() collects every value from the object into an array.

3. Does Object.entries() return an array of key-value pairs?

A. Yes ✓

B. No

Object.entries() pairs each key with its value in the array.

4. Is 'object' with a lowercase o valid for these methods?

A. No ✓

B. Yes

JavaScript requires a capital O: Object.keys().

5. Do these methods need an object passed as an argument?

A. Yes ✓

B. No

Object.keys(), values(), and entries() all need an object to inspect.

Match the Pairs

Object.keys(person) → Returns an array of person's keys

Object.values(person) → Returns an array of person's values

Returns an array pairing each key with its value → Object.entries(person)

Collects only the property names of an object → Object.keys(car)

console.log(object.keys(a)); → Wrong - 'Object' must start with a capital O

console.log(Object.Keys(b)); → Wrong - 'keys' must start with a lowercase k

Key Term

Object.keys()

Returns an array containing all the keys of a given object.

Fill in the Blanks

1. console.log(Object.keys(person));

Hint: Type the method that returns an object's keys.

2. console.log(Object.values(person));

Hint: Type the method that returns an object's values.

3. console.log(Object.entries(person));

Hint: Type the method that returns an object's key-value pairs.

4. let names = Object.keys(car);

Hint: Type the method that returns an object's keys.

5. let vals = Object.values(car);

Hint: Type the method that returns an object's values.

Spot the Error

Question 1

A console.log(object.keys(a));

B let a = {x: 1};

C console.log(a);

Line A — 'Object' must start with a capital O, not lowercase.

Question 2

A let b = {y: 2};

B console.log(Object.Keys(b));

C console.log(b);

Line B — 'keys' must be lowercase - a capital K causes an error.

Question 3

A let c = {z: 3};

B console.log(c);

C console.log(Object.values(c));

Line C — This line is actually correct - Object.values() works this way.

Question 4

A console.log(Object.Values(d));

B let d = {a: 1};

C console.log(d);

Line A — 'values' must be lowercase - a capital V causes an error.

Question 5

A let e = {b: 2};

B console.log(Object.entries(e));

C console.log(e);

Line B — This line is actually correct - Object.entries() works this way.

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