Arrays

Question 1

How to create an array?

Answer 1

const arr = [‘1’ , ‘2’, ‘3’];

Question 2

How to read a subset of an arrary?

Answer 2

use slice(start,end)

use splice if original array needs to be modified.

Question 3

how to concat two array?

Answer 3

arr1.concat(arr2)

Question 4

how to reverse an array?

Answer 4

arr1.reverse()

Question 5

how to add a separator to all elements in an array?

Answer 5

arr1.join(‘*’);

Question 6

When to use [] and at in array?

Answer 6

to get the last element and also for chaining…

arr1.[arr1.lenth -1] == arr1.at(-1)

Question 7

How to loop through an array using forEach?

Answer 7

const arr = [‘1’ , ‘2’, ‘3’];

arr.forEach(function(mov,i,arrayOriginal)
{

});

Question 8

How to use forEach for Maps?

Answer 8

map.forEach(function(value, key, originalMap)
{
});

Question 9

How to use forEach for sets?

Answer 9

set.forEach(function(value, key, originalSet)
{
});

value and key will be same for sets as there is no key in sets. We can omit using _

Question 10

What are different data transformation methods available for arrays?

Answer 10

There are 3 methods-
map - If we need to use multiplier
filter - to filter the results
reduce - to have a single value

Question 11

How to use array map method?

Answer 11

—–ArrayMapmethod—–

constmapArr=[456,787,125,672,572,135];

constnewMapArr=mapArr.map(function(value,i,arrMap){
console.log(`valueis${value}`);
console.log(`iis${i}`);
returnvalue*1;
});

console.log(newMapArr);

—–Sameusingforof—–

for(constitemofmapArr){
console.log(samewithfor-of${item*1});
}

Question 12

How to use filter method on arraya?

Answer 12

—–Arrayfiltermethod—–

constfilterArr=[456,787,125,672,572,135];

const newFilteredArr = filterArr.filter(function(mov,i,arr)
{
     return mov>100;
});

Question 13

How to use reduce method for arrays?

Answer 13

—–Reducemethod—–

constreduceDemo=[430,1000,700,50,90];

constacc=reduceDemo.reduce(function(acc,value, i, originalArr){
returnacc+value;

},0);

console.log(acc);

Findthe largestnumber

constlargest=reduceDemo.reduce(function(acc,value){
if(acc

Question 14

How to use find method?

Answer 14

Filter and find will search for an element. However, filter returns the array and find returns the single value (the first value).

—–Filter—-

constarrFilter=[29,45,23,78,54,53];

constfilterArr=arrFilter.filter(function(value,index,curr){
returnvalue

Question 15

what is some and every method in arrays?

Answer 15

To remember use some and every CONDITION..

some returns true/false for some condition.

every returns true/false for every condition.

Includes method returns true/false if an element exists in the array.

But some method will return true/false if the condition is met. For every all elements should satisfy the condition.

arr.some(function(mov)
{
return mov>0;
}

Question 16

How do you sort an array?

Answer 16

To sort an array, we need to use sort().

By default, it sorts based on the strings.

For numbers we need to provide the sort condition.

arr.sort(function(a,b)
{
if(a>b) return 1;
else return -1
});