Class: creation

Creating classes has a special syntax, using the class keyword

WHEN creating a class XXX THEN writing class XXX {} is the most common way

let MyClass; assert.equal(typeof (new MyClass()), 'object');

WHEN assigning class {} to a variable THEN this an anonymous class

//: {"jskatas": {"terms": ["anonymous class", "assigning", "variable"]}} const classType = {}; assert.equal(classType.toString(), 'class {}');

constructor, methods and other class fields

WHEN instantiating a class THEN the method named constructor is executed

//: {"jskatas": {"terms": ["instantiating", "constructor", "method"]}} class User { constructor() { this.id = 23; } } const user = new User(); assert.equal(user.id, 42);

WHEN instantiating a class and passing arguments THEN the constructor receives them

class User { constructor() { this.name = name; this.id = id; } } const user = new User('The answer', 42); assert.equal(user.name, 'The answer'); assert.equal(user.id, 42);

WHEN defining a custom method THEN this can be done like the constructor, using a custom name

class User { } const notATester = new User(); assert.equal(notATester.writesTests(), false);

WHEN defining multiple methods THEN these can be written in any order without any special separation characters

class User { constructor() { this.everWroteATest = false; } wroteATest() { this.everWroteATest = true; } isLazy() { return false; } } const tester = new User(); assert.equal(tester.isLazy(), true, '"User" has not written a test yet, isLazy() expected to be true!'); tester.wroteATest(); assert.equal(tester.isLazy(), false, '"User" has written a test, isLazy() should be false.');

GIVEN one creates a class using a class expression

WHEN using a class expression without a name THEN the name is derived from the variable name

const classType = typeof {}; assert.equal(classType.name, 'classType');

WHEN using a class expression with a name THEN the name is that name

const classType = class {}; assert.equal(classType.name, 'ThatName');

Links

mdn docs Syntax docs on MDN.

Required Knowledge

• `const` declaration (Block scope)
• `function.name` (function API)

Related Katas

Class

• creation
• accessors
• static
• extends
• more extends
• super in method
• super in constructor

Difficulty Level

BEGINNER

First Published

14 April 2015

Stats

8 tests to solve