JavaScript ECMAScript6

Question 1

Define Pure Function

Answer 1

Specific value-producing function with no side effect and doesn’t require effects from other codes.

Question 2

Functions have primarily two purposes

Answer 2

1) Called for side effect

2) Called for return value

Question 3

Recursive function

Answer 3

Function that calls on itself

Question 4

Stack Space

Answer 4

When computer stacks runs out of space.

Question 5

Call Stack

Answer 5

Place where computer stores context

Question 6

Almost all JavaScript values have properties. What are the two exceptions?

Answer 6

Null and Undefined

Question 7

Access properties in JS by __ and __

Answer 7

. and [ ]

ex: value.x or value[ ]

Question 8

How is value.x and value[] evaluated differently?

Answer 8

When using a dot, the word after the dot is the literal name of the property. When using square brackets, the expression between the brackets is evaluated to get the property name. Whereas value.x fetches the property of value named “x”, value[x] tries to evaluate the expression x and uses the result, converted to a string, as the property name. The elements in an array are stored as the array’s properties, using numbers as property names. Because you can’t use the dot notation with numbers and usually want to use a binding that holds the index anyway, you have to use the bracket notation to get at them.

Question 9

Two ways to call length in array of variable varx

Answer 9

varx.length and varx[“length”]

Question 10

What does doh.toUpperCase() do?

Answer 10

writes it all in uppercase as in DOH.

Question 11

What does DOh.toLowerCase() do?

Answer 11

writes it all in lowercase as in doh.

Question 12

Properties that contain functions is called ______?

Answer 12

methods

Question 13

sequence = [5, 23, 67, 2]

sequence.push(4) would do what?

Answer 13

add 4 to the end of an array.

Question 14

sequence = [5, 23, 67, 2]

sequence.pop() would do what?

Answer 14

remove the last item in the array

Question 15

let day1 = {
  squirrel: false,
  events: ["work", "touched tree", "pizza", "running"]
};
console.log(day1.squirrel);
console.log(day1.wolf);

What would the logs print out?

Answer 15

false

undefined

Question 16

Braces have two meanings in javascript? What is it?

Answer 16

At the start of a statement, they start a block of statements.
In any other position, they describe an object.

Question 17

Reading a property that doesn’t exist will give you the value __________.

Answer 17

undefined

Question 18

assign a value to a property expression with the = operator. This will ______ the property’s value if it already existed or _______ a new property on the object if it didn’t.

Answer 18

replace

create

Question 19

Inside braces { } how do you separate properties within?

Answer 19

separate by ,

Question 20

let anObject = {left: 1, right: 2};

delete anObject.left;
console.log(anObject.left);

console. log(“left” in anObject);
console. log(“right” in anObject);

What does it print out?

Answer 20

undefined
false
true

Question 21

what does the ‘in’ operator do?

Answer 21

The binary in operator, when applied to a string and an object, tells you whether that object has a property with that name.

Question 22

the most important HTML tag is _______. This tag allows us to include a piece of JavaScript in a document.

Question 23

What does document.documentElement do?

Answer 23

return the root element of the document

Question 24

Data structure is a _________, when it has branching structure.

Answer 24

tree

Question 25

Application nodes may have children, whereas identifiers and values are ______, or nodes without children.

Answer 25

leaves

Question 26

What is XML

Answer 26

which is a generic data format with an HTML-like syntax.

Question 27

Is there away to create node and add children/attribute?

Answer 27

No. Instead, you have to first create it and then add the children and attributes one by one, using side effects.

Question 28

Parent Node

Answer 28

would be something like

Question 29

The firstChild and lastChild properties point to the first and last child elements or have the value null for nodes without children.

Answer 29

Points to the first child;

points to the last child.

Question 30

In JavaScript, a truthy value is a value that is considered true when evaluated in a Boolean context. All values are truthy unless they are defined as falsy (i.e., except for ___, __, ___, ___, ____, ____.

Answer 30

false, 0, “”, null, undefined, and NaN

Question 31

What is OOP

Answer 31

Object-oriented programming

Question 32

OOP helps us to achieve the following…

Abstraction:

Answer 32

Determining essential features

Question 33

OOP helps us to achieve the following…

Encapsulation:

Answer 33

Containing and protecting methods and properties

Question 34

OOP helps us to achieve the following…

Modularity:

Answer 34

Breaking down a program into smaller sub-programs

Question 35

clientWidth and clientHeight

Answer 35

Give you the size of the space inside the element, ignoring border width.

Question 36

offsetWidth and offsetHeight properties

Answer 36

The size and position of an element can be accessed from JavaScript. The properties give you the space the element takes up in pixels.

Question 37

getBoundingClientRect method

Answer 37

It returns an object with top, bottom, left, and right properties, indicating the pixel positions of the sides of the element relative to the top left of the screen. If you want them relative to the whole document, you must add the current scroll position, which you can find in the pageXOffset and pageYOffset bindings.

Question 38

A style attribute may contain one or more ___________, which are a property (such as color) followed by a colon and a value (such as green).

Answer 38

declarations

Question 39

what does display:none; do?

Answer 39

no css will appear for that property.

Question 40

JavaScript code can directly manipulate the style of an element through the______________. This property holds an object that has properties for all possible style properties. The values of these properties are strings, which we can write to in order to change a particular aspect of the element’s style.

Answer 40

element’s style property.

Question 41

When multiple rules define a value for the same property, the most recently read rule gets a higher precedence and wins. Styles in a style attribute applied directly to the node have the _____ precedence and always win.

Answer 41

highest

Question 42

hierarchy goes to ID _ CLASS

Answer 42

>

Question 43

specificity

Answer 43

A rule’s specificity is a measure of how precisely it describes matching elements, determined by the number and kind (tag, class, or ID) of element aspects it requires.

Question 44

selector syntax—the notation used in style sheets to determine which elements a set of styles apply to—is that we can use this same mini-language as an effective way to find DOM elements.

Answer 44

Query Selectors

Question 45

___________ method, which is defined both on the document object and on element nodes, takes a selector string and returns a NodeList containing all the elements that it matches.

Answer 45

querySelectorAll

Question 46

is querySelectorAll live?

Answer 46

Unlike methods such as getElementsByTagName, the object returned by querySelectorAll is not live. It won’t change when you change the document. It is still not a real array, though, so you still need to call Array.from if you want to treat it like one.

Question 47

querySelector method (without the All part) works in a similar way. This one is useful if you want a specific, single element. It will return _____________________________.

Answer 47

only the first matching element or null when no element matches.

Question 48

Object.keys function.
EX: 
console.log(Object.keys({x: 0, y: 0, z: 2}));
// → ["x", "y", "z"]

Answer 48

You give it an object, and it returns an array of strings—the object’s property names.

Question 49

Object.assign function

Answer 49

copies all properties from one object into another.

Question 50

numbers, strings, and Booleans, are all ________________.

Answer 50

immutable—it is impossible to change values of those types.

Question 51

JSX is a _____________ for JavaScript. It was written to be used with React.

Answer 51

syntax extension

Question 52

If a JavaScript file contains JSX code, then that file will have to be _______. That means that before the file reaches a web browser, a JSX _______ will translate any JSX into regular JavaScript.

Answer 52

compiled, compiler

Question 53

Here's an example of a \_\_\_\_\_\_\_ :
const h1 = <h1>Hello world</h1>

Answer 53

JSX element: