TypeScript basics 1

How does a TypeScript class implement an interface?

• class MyCoolClass implements IMyCoolInterface {

  }

• class MyCoolClass extends IMyCoolInterface {

  }

• interface IMyCoolInterface implemented by MyCoolClass {

  }

• A class implements an interface automatically.

2) What is the benefit of interfaces?

• They let you hide what the class is and reference an object via the interface.

• They let you define inline-objects with type safety, like so:

  
  

  let myObject: IMyCoolInterface = {

  myCoolVariable: 1

  }

• They let you change assign a different class to a variable as long as it implements the same interface.

• All of the above.

TypeScript is all about specifying what type your variable or return value is. Is is possible to define

a variable in TypeScript without a type? Like so:

let a

and not:

let a: number

• Yes type is optional (for interoperability with JavaScript)

• No, type is always required (knowing types always helps prevent bugs)

What type of variable is this:

var version: {

subVersion: number

};

• boolean

• number

• object

• string

What is a difference between the following:

let a = 0;

const a = 0;

• "const a" can be reassigned. "let a" cannot be reassigned.

• "let a" can be reassigned. "const a" cannot be reassigned.

• There is no difference

How do you declare a variable inside a class?

• class MyCoolClass {

  let myCoolVariable;

  }

• class MyCoolClass {

  myCoolVariable;

  }

How do you declare a method inside a class?

• class MyCoolClass {

  function myCoolMethod() {

  }

  }

• class MyCoolClass {

  myCoolMethod() {

  }

  }

How to you declare paramaters in a functions (or class methods)?

• Between square brackets, comma delimited:

  
  

  function myCoolFunction[

  parameterA,

  parameterB

  ] {

  }

• Between parentheses, each on its own line:

  
  

  function myCoolFunction(

  parameterA

  parameterB

  ) {

  }

• Between square brackets, each on its own line:

  
  

  function myCoolFunction[

  parameterA

  parameterB

  ] {

  }

• Between parentheses, comma delimited:

  
  

  function myCoolFunction(

  parameterA,

  parameterB

  ) {

  }

How do you declare type of parameters of a method (or a function)?

• Put the type after the parameterName:

  
  

  class MyCoolClass {

  myCoolMethod(

  myCoolParameter number

  ) {

  }

  }

• Put the type after the parameterName and add a colon in between:

  
  

  class MyCoolClass {

  myCoolMethod(

  myCoolParameter: number

  ) {

  }

  }

• Put the type before the parameterName:

  
  

  class MyCoolClass {

  myCoolMethod(

  number myCoolParameter

  ) {

  }

  }

• Put the type before the parameterName and add a colon in between:

  
  

  class MyCoolClass {

  myCoolMethod(

  number: myCoolParameter

  ) {

  }

  }

How to you declare the return type of a function (or a method)?

• Put the return type after the parameter list and add a colon in between:

  
  

  function myCoolFunction(): boolean {

  return true;

  }

• Put the return type after the parameter list:

  
  

  function myCoolFunction() boolean {

  return true;

  }

• Put the return type before the function/method name and add a colon in between:

  
  

  function boolean:myCoolFunction() {

  return true;

  }

• Put the return type before function/method name:

  
  

  function boolean myCoolFunction() {

  return true;

  }