Language

Question 1

What is Code?

Answer 1

Code is the text that makes up programs.

Question 2

What is an Expression?

Answer 2

A fragment of code that produces a value. Every value that is written literally is an expression.

Question 3

What is a Statement?

Answer 3

If an expression corresponds to a sentence fragment, a JavaScript statement corresponds to a full sentence. A program is a list of statements.

If an expression corresponds to a sentence fragment, a JavaScript statement corresponds to a full sentence. A program is a list of statements.

Question 4

What is a Binding?

Answer 4

To catch and hold values, JavaScript provides a thing called a binding, or variables.

Question 5

What is the Environment?

Answer 5

The collection of bindings and their values that exist at a given time is called the environment.

Question 6

What is a Function?

Answer 6

A function is a piece of program wrapped in a value. Such values can be applied in order to run the wrapped program.

Question 7

What is a Program?

Answer 7

A program is a collection of statements, which contain expressions that are executed from top to bottom.

Question 8

What is scope?

Answer 8

The part of the program where the binding is visible.

Question 9

What is lexical scoping

Answer 9

The set of bindings visible inside a block is determined by the place of that block in the program text. Each local scope can also see all the local scopes that contain it, and all scopes can see the global scope. This approach to binding visibility is called lexical scoping.

Question 10

What is Closure?

Answer 10

A feature of a function that allows there to be a reference to a specific instance of a local binding in an enclosing scope.

Question 11

What is an example of Closure?

Answer 11

function multiplier(factor) {
return number => number * factor;
}
 let twice = multiplier(2);
console.log(twice(5));
// → 10

Question 12

What is Recursion?

Answer 12

A function that calls itself.

Question 13

What is an example of a recursive function?

Answer 13

function findSolution(target) {
  function find(current, history) {
    if (current == target) {
      return history;
    } else if (current > target) {
      return null;
    } else {
      return find(current + 5, `(${history} + 5)`) ||
             find(current * 3, `(${history} * 3)`);
    }
  }
  return find(1, "1");

Question 14

What is control flow?

Answer 14

Enables us to decide which lines are run based on our code base.

Question 15

What is coercion?

Answer 15

A way in which we can implicitly or explicitly change the value of datatypes.

Question 16

What does lexically scoped mean?

Answer 16

The location at which a variable is declared determines its scope.

Question 17

What is a ReferenceError?

Answer 17

An error where the program could not find any reference to the variable; possible the variable doesn’t exist.

Question 18

What is a compiler?

Answer 18

A compiler is a program that converts your Java program into code called bytecode.

• checks program for syntax errors
• generates a new program that is readable by the language.

Question 19

What does the diagram for the Java Runtime Environment look like?

Answer 19

1. Source code: ‘human readable code’ = file extension.”java”;
2. Compiler
3. Bytecode: ‘JVM readable code’ = file extension.”class”
4. Windows, Mac, Linux

Question 20

What is OOP?

Answer 20

Object-oriented programming is an approach to programming that uses the concept of classes and objects.

Question 21

What are three kinds of scopes?

Answer 21

Global Scope, Function Scope, and Block Scope (created by ‘let’)

Question 22

What is projection?

Answer 22

Applying a function to a value and creating a new value is called a projection. To project one array into another, we apply a projection function to each item in the array and collect the results in a new array.

Question 23

What is React?

Answer 23

React is a JavaScript library used for building user interfaces.

Question 24

What is Redux in terms of React?

Answer 24

A way to manage state within React.

Question 25

What is z-index?

Answer 25

The z-index property specifies the stack order of an element. An element with greater stack order is always in front of an element with a lower stack order.

Question 26

What does URL stand for?

Answer 26

Uniform Resource Locator

Question 27

What is a closure?

Answer 27

A function contained within a function where the inner function has access to the scope of the enclosing outer function.

Question 28

What is hoisting?

Answer 28

When a function and variable declarations are added to memory during the compile phase.
Hoisting is usually defined as “declarations being moved to top of your code” because that’s what seems to be happening but the code doesn’t actually physically move to the top of the file.

Question 29

What are side effects?

Answer 29

A side effect is any application state change that is observable outside the called function other than its return value.

Question 30

What is a syntax parser?

Answer 30

A program that reads your code and determines if its function and the validity of its grammar.

Question 31

What is lexical environment?

Answer 31

Where something sits physically in the code you write.

Question 32

What is execution context?

Answer 32

A wrapper to help manage the code that is running.

Question 33

What is single-threaded synchronous execution?

Answer 33

One at a time and in order, JavaScript runs its code this way.

Question 34

What is variable environment?

Answer 34

Where the variables live in memory and how they relate to each other.

Question 35

What is Asynchronous?

Answer 35

More than one at a time.

Question 36

What is Event Queue?

Answer 36

Javascript runs this once the call stack is empty. It’s a stack of events that are placed in order from the browser.

Question 37

What is a Primitive Type?

Answer 37

A type of data that represents a single value; that is not an object.

Question 38

What are the 6 Primitive types?

Answer 38

1. Undefined
2. Null
3. Boolean
4. Number
5. String
6. Symbol

Question 39

What is Operator Precedence?

Answer 39

The order of operation for comparison operators (PEMDAS)

Question 40

What is a namespace?

Answer 40

A container for variables and functions. Typically to keep variables and functions with the same name separate. (Not needed in JS)

Question 41

What is First Class Functions?

Answer 41

The concept that everything you can do with other data types, you can do with functions.

Question 42

What is IIFE?

Answer 42

Immediately Invoked Function Expression - when a function is invoked immediately after creating it.

Question 43

What is function currying?

Answer 43

Creating a copy of a function, but with some preset parameters. (Very useful in mathematical calculations.)

Question 44

What are the steps to tackling a problem?

Answer 44

How do we define the problem?
What are the possible solutions?
Which solution best meets our constraints? What are the instruction steps to implement the solution?
Does the solution produce the desired output?
Can we make this solution more elegant or optimal?

Question 45

What is the back end?

Answer 45

Any application or set of applications connected to the internet, who’s primary purpose is to service client requests.

Question 46

What is a framework?

Answer 46

A hierarchical directory that encapsulates shared resources, which can include dynamic shared libraries, etc.

Question 47

What is transpile?

Answer 47

To convert the syntax of one programming language to another.

Question 48

What is refactoring?

Answer 48

The process of restructuring existing code without changing its external behavior.

Question 49

What is event delegation?

Answer 49

A method that avoids adding Event Listeners to individual child nodes and instead adds it to the parent node who selects the child node.

Question 50

What is the syntax of a regular expression?

Answer 50

pattern/ modifier
regex = /ou/i
pattern = ou
modifier = i (case sensitive)

Question 51

What are regex simple patterns?

Answer 51

Constructs where you want to find a direct match.

Question 52

What is the regex match method?

Answer 52

Looks for the first match in a construct and exits the search.
var repeat = 'abc abc abc abc';
var regex = /abc/i
repeat.match(regex)
returns // 1 match

Question 53

What does a global modifier do in regex?

Answer 53

Finds every instance throughout the variable, unlike match.
var regex = /abc/ig

Question 54

What is the search method in a regex?

Answer 54

Used to look for a regex in a string…returns the index of the first instance…

Question 55

What is a pure function?

Answer 55

A function that * given the same input, always returns the same output * produces no side effects * relies on no external state

Question 56

What is the syntax for a filter function?

Answer 56

array.filter(function(current value) { return true; });

Question 57

What is the syntax for a reduce function?

Answer 57

array.reduce(function(acc, curr, index, array) {

return acc + curr;} , 0);

Question 58

How do you map a non-word character in regex?

Answer 58

Use ‘w’ as in /\W/ it matches any alphanumeric character

Question 59

Adding a ‘?’ character does what to a regex?

Answer 59

It matches 0 or 1 of the previous character.

toy ?boats?
toyboats will return true

Question 60

What does \s match in regex?

Answer 60

Whitespace characters

Question 61

What matches any character in regex?

Answer 61

the ‘ . ‘ character

Question 62

What is the difference between ‘ + ‘ and ‘ * ‘ in regex?

Answer 62

The ‘ * ‘ wants to match 0 or more characters
toy\w*
The ‘ + ‘ wants to match at least 1 or more characters after it

Question 63

How are repetitions matched in regex?

Answer 63

By using square brackets {3}; putting a coma after the number {3, } will match 3 or more repetitions; and adding a second number {3, 5} will match between 3 and 5.

Question 64

How do you match exceptions in regex?

Answer 64

Using a ^ before the character you want to exclude will match: [^ character]
[^@]
toy@boat
will match: toy boat

Question 65

How are capitalizations managed in regex?

Answer 65

\s = whitespace  ||   \S = NOT whitespace
\d = digits            ||   \D = NOT digits
\w = word            ||    \W = NOT word

Question 66

What are the flags in regex?

Answer 66

i matches case-insensitive
g matches global
m matches multiline

Question 67

What kinds of nodes are there in the DOM tree?

Answer 67

1. DOM Nodes
2. Element nodes == 1
3. Text Nodes == 3
4. Comment Nodes == 8

Question 68

What is the value of ‘this’ in a FFE?

Answer 68

In a Free Function Invocation, ‘this’ refers to the window object, which is global.

Question 69

What is the __proto__ property of Object.prototype?

Answer 69

An accessor property( a getter and setter function) that
exposes the [[Prototype]] of the internal object through which it is accessed. The __proto__ property is a pointer to another object that has several properties on it.

1. Every object has a __proto__ property.
2. The __proto__ of an object literal is equal to Object.prototype.
3. The __proto__ of Object.prototype is null.

Question 70

What does the ‘rest’ operator do?

Answer 70

The ‘rest’ operator collects the tail end of the items and collects them into an array.

Question 71

What does the ‘spread’ operator do?

Answer 71

The ‘spread’ operator can spread out items of an array into another array and properties of an object into another object.

Question 72

What are the 6 rules to the ‘this’ binding?

Answer 72

1. If the ‘new’ keyword is used when calling the function, ‘this’ inside the function is a brand new object.
2. If apply, call, or bind are used to call a function, ‘this’ inside the function is the object that is passed in as an argument.
3. If dot notation is used to invoke a function (called as a method), ‘this’ is an object that the function is a property of.
4. If a function is invoked as a Free Function Invocation, ‘this’ is the global object.
5. If multiple rules apply, the rule that is higher wins.
6. If the function is ES2015, it ignores all of the above and receives the ‘this’ value of its surrounding scope at the time it’s created.

Question 73

What is inheritance?

Answer 73

Inheritance refers to an object’s ability to access methods and other properties from other objects.

Question 74

What are the 4 pillars of OOP?

Answer 74

Encapsulation, Abstraction, Inheritance, and Polymorphism

Question 75

What is Encapsulation in OOP?

Answer 75

It describes the idea of bundling data and methods that work on that data in a single unit.

Question 76

What is Abstraction in OOP?

Answer 76

The process that allows programmers to hide all but the relevant data about an object in order to reduce complexity and increase efficiency.

Question 77

What is Inheritance in OOP?

Answer 77

A mechanism that allows you to eliminate redundant code by allowing new objects to take on the properties of existing objects.

Question 78

What is Polymorphism in OOP?

Answer 78

It means many forms: the ability of different objects to respond, in its own way, to identical messages.

Question 79

What is the difference between Class vs Prototypal inheritance?

Answer 79

A class is a blueprint (description of the item to be created). A prototype is a working object instance…objects inherit directly from other objects.

Question 80

What is the difference between prototype vs instance members?

Answer 80

Instance members are when methods are created inside of objects. Prototype members allow for methods to be overwritten and added by using Circle.prototype.method = function() {console.log(‘desired output’);}

Question 81

How do you get the prototype of an object?

Answer 81

Object.getPrototypeOf(obj);

Question 82

What is the keyword to get the attributes of a property on an object?

Answer 82

Object.getOwnPropertyDescriptor(obj, ‘propertyName’);

Question 83

How do you set the attributes for a property?

Answer 83

Object.defineProperty(obj, ‘propertyName’, {configurable: false // can’t be deleted, writable: false // read-only, enumerable: false})

Question 84

What does the constructor ‘prototype’ property do?

Answer 84

It returns the object that will be used as the prototype for the objects created by the constructor. Object.prototype === Object.getPropertyOf({}); // true

Question 85

How do you create a prototypal inheritance?

Answer 85

ChildObj.prototype = Object.create(ParentObj.prototype);

• must also reset the constructor:
  ChildObj.prototype.constructor = ChildObj;

Question 86

What must happen when you want to call properties from the Super constructor?

Answer 86

You must bind the Super using the .call method:

ParentObj.call(this, attribute);

Question 87

What is intermediate function inheritance?

Answer 87

It’s when the extend function is used to create an inheritance in order to avoid repetitive code.

Question 88

How are methods overwritten?

Answer 88

Using ChildObj.prototype.method = function() {desired function};

The JS Engine will walk up the prototype chain and find the closest method to implement.

Question 89

How do we sort the odds without moving the evens in an array?

Answer 89

function sortArray(array) {
  const odd = array.filter((x) => x % 2).sort((a,b) => a - b);
  console.log(odd + ' is odd')
  return array.map((x) => {
    return x % 2 ? odd.shift() : x
    });
}
sortArray(nums)

Question 90

How do we filter the difference of two arrays?

Answer 90

function array_diff(a, b) {
  const filtered = []

if(a.length === 0 || b.length === 0) return a;
else {
return a.filter((item) => !b.includes(item))
}
}

Question 91

How do we use async setImmediate pattern?

Answer 91

function doAsyncTask(cb) {
  cb();
}
doAsyncTask(_ => console.log(message));

let message = “Callback Called”;

Question 92

How do we code async process.nextTick patterns?

Answer 92

function doAsyncTask(cb) {

process.nextTick(() => {
console.log(“Async Task Calling Callback with Process”);
cb();
})

}
doAsyncTask(_ => console.log(message));

let message = “Callback Called”;

Question 93

What are the Asynch Patterns in JS?

Answer 93

setInterval(() => {});
setTimeout(() => {});
setImmediate(() => {});
process.nextTick(() => {});
readFile(() => {});

Question 94

What is the syntax for a Promise?

Answer 94

function doAsynchTask() {

let error = false;
const promise = new Promise( (resolve, reject) => {
   setTimeout(() => {
   console.log("Asynch Work Complete");
   if (error) {
        reject();
     } else {
         resolve();
     }   
   }, 1000);
});

return promise;
}

Question 95

How do we create a Promise notification?

Answer 95

Attach a success handler to its then function.

doAsynchTask().then(
() => console.log(“Task Complete”) ,
() => console.log(“Task Errored!”)
);

OR if there’s an error
use a second argument in the then function.