Basics

Question 1

Arrow functions

Answer 1

let addTwoNums = (n1,n2) => n1+n2;

Question 2

forEach in array

Answer 2

let nums = [10, 20, 30];
nums.forEach((number, index, array) => {
console.log(number)
});
Note: number is an element of array, 
index and array are optional.

nums.forEach(function(number) {
console.log(number);
});

Question 3

For - of: iterate over an array

Answer 3

for (const myElement of myArray) {
console.log(myElement);
}

Question 4

Add an element to an array

Answer 4

PUSH(): add an element to at the END of an array

UNSHIFT(): adds it at the BEGINNING of an array

Question 5

Removal elements from arrays

Answer 5

POP(): remove the last element of an array

SPLICE(index from which to begin removing, number of elements to remove)

Question 6

Sort()

Answer 6

const numbers =[3, 23,12]
let sorted = numbers.sort((a,b) => a-b); // 3,12,23

let sorted_desc = numbers.sort((a, b) => b-a); // 23, 12, 3

Question 7

filter()

Returns a new array

Answer 7

let cities = [
{ name: “Los Angeles”, population: 3700000 },
{ name: “New York”, population: 8175133 },
{ name: “Chicago”, population: 2695598 },
{ name: “Houston”, population: 2099451 },
{ name: “Philadelphia”, population: 1526006 },
];

// FILTER() returns a new array with all elements that pass the test implemented by the callback() function
// eg: arrayObject.filter(callback, contextObject);
// another way using filter()
let bigCities = cities.filter((city) => city.population > 3000000);
console.log(bigCities1);

Question 8

Reduce()

Answer 8

// acc: accumulator; c: current value; 0: starting value of accumulator

let numArr = [11, 35, 67, 14, 78, 10];
let sum = numArr.reduce((acc, c) => acc + c, 0);
console.log(sum);

Question 9

In JavaScript, a function is a value, so we can deal with it as a value.

Answer 9

function sayHi() {
  alert( "Hello" );
}

alert( sayHi ); // shows the function code

Please note that the last line does not run the function, because there are no parentheses after sayHi. There are programming languages where any mention of a function name causes its execution, but JavaScript is not like that.

Question 10

function sayHi() {   // (1) create
  alert( "Hello" );
}

let func = sayHi; // (2) copy

func(); // Hello     // (3) run the copy (it works)!
sayHi(); // Hello    //     this still works too (why wouldn't it)

Answer 10

The Function Declaration (1) creates the function and puts it into the variable named sayHi.
Line (2) copies it into the variable func. Please note again: there are no parentheses after sayHi. If there were, then func = sayHi() would write the result of the call sayHi() into func, not the function sayHi itself.
Now the function can be called as both sayHi() and func().

Question 11

Array constructor with multiple parameters

Answer 11

let fruits = new Arrat(‘apple’, ‘banana’);

console. log(fruits.length); //2
console. log(fruits[0]); //‘apple’

Example 2:

let colors = new Array(2);

console. log(colors.length); //2
console. log(colors[0]); //undefined

Question 12

Linking to Same Page in HTML

Answer 12

In order to link to a target on the same page, we must give the target an ID.
EXAMPLE:

<p>This is the top of the page</p>

<p></p>

<h1>This is the bottom!</h1>

The target link is a string containing the octothorpe # character and the target element’s id.

<ol>
<li><a>Top</a></li>
<li><a>Bottom</a> </li></ol>

Question 13

Linking to relative page.
Files are store on the same folder-> can use a relative path
Eg: ./index.html

Answer 13

<a>Contact</a>