How can you share code between files?

 

 

On the client (browser environment), as long as the variables/functions are declared in the global scope (window), all scripts can refer to them. Alternatively, adopt the Asynchronous Module Definition (AMD) via RequireJS for a more modular approach.

On the server (Node.js), the common way has been to use CommonJS. Each file is treated as a module and it can export variables and functions by attaching them to the module.exports object.

ES2015 defines a module syntax which aims to replace both AMD and CommonJS. This will eventually be supported in both browser and Node environments.

What are the benefits of using spread syntax and how is it different from rest syntax? 

 

 

 

function putDookieInAnyArray(arr) {
  return [...arr, 'dookie'];
}

const result = putDookieInAnyArray(['I', 'really', "don't", 'like']); 
  // ["I", "really", "don't", "like", "dookie"]

const person = {
  name: 'Todd',
  age: 29,
};

const copyOfTodd = { ...person };

Can you give an example for destructuring an object or an array?

 

Array destructuring

// Variable assignment.
const foo = ['one', 'two', 'three'];

const [one, two, three] = foo;
console.log(one); // "one"
console.log(two); // "two"
console.log(three); // "three"
// Swapping variables
let a = 1;
let b = 3;

[a, b] = [b, a];
console.log(a); // 3
console.log(b); // 1
Object destructuring

// Variable assignment.
const o = { p: 42, q: true };
const { p, q } = o;

console.log(p); // 42
console.log(q); // true

What is the definition of a higher-order function?

 

 

 

A higher-order function is any function that takes one or more functions as arguments, which it uses to operate on some data, and/or returns a function as a result.

Higher-order functions are meant to abstract some operation that is performed repeatedly. The classic example of this is map, which takes an array and a function as arguments. map then uses this function to transform each item in the array, returning a new array with the transformed data. Other popular examples in JavaScript are forEach, filter, and reduce. A higher-order function doesn't just need to be manipulating arrays as there are many use cases for returning a function from another function. Function.prototype.bind is one such example in JavaScript.

What advantage is there for using the arrow syntax for a method in a constructor?

The main advantage of using an arrow function as a method inside a constructor is that the value of this gets set at the time of the function creation and can't change after that. So, when the constructor is used to create a new object, this will always refer to that object. For example, let's say we have a Person constructor that takes a first name as an argument has two methods to console.log that name, one as a regular function and one as an arrow function:

 

 

Explain the difference between synchronous and asynchronous functions.

 

 

Synchronous functions are blocking while asynchronous functions are not. In synchronous functions, statements complete before the next statement is run. In this case, the program is evaluated exactly in order of the statements and execution of the program is paused if one of the statements take a very long time.

Asynchronous functions usually accept a callback as a parameter and execution continue on the next line immediately after the asynchronous function is invoked. The callback is only invoked when the asynchronous operation is complete and the call stack is empty. 

What language constructions do you use for iterating over object properties

 

 

  • for-in loops - for (var property in obj) { console.log(property); }. However, this will also iterate through its inherited properties, and you will add an obj.hasOwnProperty(property) check before using it.
  • Object.keys() - Object.keys(obj).forEach(function (property) { ... }). Object.keys() is a static method that will lists all enumerable properties of the object that you pass it.
  • Object.getOwnPropertyNames() - Object.getOwnPropertyNames(obj).forEach(function (property) { ... }). Object.getOwnPropertyNames()
  • is a static method that will lists all enumerable and non-enumerable properties of the object that you pass it.

What language constructions do you use for iterating over Array

 

  • for loops - for (var i = 0; i < arr.length; i++). The common pitfall here is that var is in the function scope and not the block scope and most of the time you would want block scoped iterator variable. ES2015 introduces let which has block scope and it is recommended to use that instead. So this becomes: for (let i = 0; i < arr.length; i++).
  • forEach - arr.forEach(function (el, index) { ... }). This construct can be more convenient at times because you do not have to use the index if all you need is the array elements. There are also the every and some methods which will allow you to terminate the iteration early.
  • for-of loops - for (let elem of arr) { ... }

Done

What is JSONP

 

JSONP (JSON with Padding) is a method commonly used to bypass the cross-domain policies in web browsers because Ajax requests from the current page to a cross-origin domain is not allowed.

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