✅ Solution: Javascript Arrays Interview Questions

Create an Array object - (Atleast 3 methods) - Explanation Video

Method - #1

var fruits = ["Apple", "Banana"];
console.log(fruits); // [ 'Apple', 'Banana' ]

Method - #2

var msgArray = [];
msgArray[0] = "Hello";
console.log(msgArray); // [ 'Hello' ]

Method - #3

var array = new Array("Hello");
console.log(array); // [ 'Hello' ]

Method - #4

var another = Array.of(1, 2, 3);
console.log(another); // [ 1, 2, 3 ]

Take the below array and copy it using the slice method and the for loop method. - Explanation Video

var array = [1, 2, 3, 4, 5];

Method - #1 (The slice method)

var array = [1, 2, 3, 4, 5, 6];

var result = array.slice(); // to copy an array to new array

console.log(array); // [1,2,3,4,5,6]
console.log(result); // [1,2,3,4,5,6]

Method - #2 (The for loop method)

var array = [1, 2, 3, 4, 5, 6];
var array2 = [];

for (var i = 0; i < array.length; ++i) {
  array2[i] = array[i];
}

console.log(array2); // [ 1, 2, 3, 4, 5, 6 ]

Empty this array: - Explanation Video

var array = [1, 2, 3, 4, 5];

✔️ Solution - Method - #1 (The for loop method)

var array = [1, 2, 3, 4, 5];

Array = [];

This is only recommended if you don't have any other references to this array because it will actually create a new empty array and the other reference will still be available to others in memory.

For Example:

var array = [1, 2, 3, 4, 5];
var array2 = array;

array = [];

console.log(array); // [ ];
console.log(array2); // [ 1, 2, 3, 4, 5 ]

✔️ Solution - Method - #2

var array3 = [1, 2, 3, 4, 5];
array3.length = 0;
console.log(array3); // [ ];

This even empties to referenced arrays

var array3 = [1, 2, 3, 4, 5];
var array4 = array3;
array3.length = 0;
console.log(array3); // [ ];
console.log(array4); // [ ];

✔️ Solution - Method - #3

var array5 = [1, 2, 3, 4, 5];
array5.splice(0, array5.length);
console.log(array5); // [ ];

✔️ Solution - Method - #4

var array6 = [1, 2, 3, 4, 5];
console.log(array6); // [1,2,3,4,5]

function emptyArray(array) {
  "use strict";
  while (array.length) {
    array6.pop();
  }
}

emptyArray(array6); // call function
console.log(array6); // [ ] ; now empty

What type is an Array set to?

var array3 = [1, 2, 3, 4, 5];
console.log(typeof array3); // Object

How can you check if something is an Array?

✔️ Solution - Method - #1

var check = [1, 2, 3];
var a = Array.isArray([1, 2, 3]);
var b = Array.isArray({
  foo: 123,
});
var c = Array.isArray("foobar");
var d = Array.isArray(undefined);
var e = Array.isArray(check);

console.log(a); // true
console.log(b); // false
console.log(c); // false
console.log(d); // false
console.log(e); // true

✔️ Solution - Method - #2

function checkIfArray(array) {
  "use strict";

  if (Object.prototype.toString.call(array) === "[object Array]") {
    console.log("array it is  ");
  } else {
    console.log("array it is Not ");
  }
}

var array2 = "testing";
checkIfArray(array2); // array it is Not
var array3 = [1, 2, 3, 4, 5];
checkIfArray(array3); //array it is

✔️ Solution - Method - #3

var array = [1, 2, 3, 4, 5];

function checkIfArray(object) {
  "use strict";
  if (typeof object === "string") {
    console.log("array it is NOT ");
  } else {
    console.log("array it is ");
  }
}

checkIfArray(array); //array it is

Add an item to the end of an array.

✔️ Solution - Method - #1

var array = ["a", "b", "c"];

array.push("d");
console.log(array); // [ 'a', 'b', 'c', 'd' ]

✔️ Solution - Method - #2

array[array.length] = "e";
console.log(array); // [ 'a', 'b', 'c', 'd', 'e' ]

Find the index position of d in this array

var arr = ["a", "b", "c", "d"];

✔️ Solution:

console.log(arr.indexOf("d")); // 3

What will be returned if you look for the index of something that does not exist?

✔️ Solution:

var arr = ["a", "b", "c", "d"];
console.log(arr.indexOf(7)); // -1 === does not exist

Write a function to check if milk exists in your array.

var items = ["milk", "bread", "sugar"];

✔️ Solution:

var items = ["milk", "bread", "sugar"];

function checkForProduct(item) {
  if (items.indexOf(item) === -1) {
    console.log("item does not exist");
  } else {
    console.log("item is in your list");
  }
}

checkForProduct("socks"); //item does not exist
checkForProduct("milk"); //item is in your list

Now you've found milk exists add some code to find the index of milk and remove that item.

✔️ Solution:

var items = ["milk", "bread", "sugar"];

//find index of item if it exists
var a = items.indexOf("milk");
console.log(a); // 0

//remove that index from array
items.splice(0, 1);
console.log(items); // [ 'bread', 'sugar']

List the ways to loop over an array.

✔️ Solution:

For Each
For-in
For loop
For-of

Write some code to put these numbers in order (Ascending & Descending)

var numbers = [1, 12, 2, 23, 77, 7, 33, 5, 99, 234];

✔️ Solution:

var numbers2 = [1, 12, 2, 23, 77, 7, 33, 5, 99, 234];
var numbers3 = numbers2.sort((a, b) => {
  return a - b;
});

console.log(numbers3); // [ 1, 2, 5, 7, 12, 23, 33, 77, 99, 234 ]

Write some code to place this list in alphabetical order

var p = ["a", "z", "e", "y"];

✔️ Solution:

var p = ["a", "z", "e", "y"];

p.sort();

console.log(p); // [ 'a', 'e', 'y', 'z' ]

What is the length of these arrays

var arr1 = [, , ,];

var arr2 = new Array(3);

var arr3 = [1, 2, 3, 4, 5];

var array = [
  [1, 2, 3],
  [4, 5, 6],
];

✔️ Solution:

var arr1 = [, , ,];

var arr2 = new Array(3);

var arr3 = [1, 2, 3, 4, 5];

var array = [
  [1, 2, 3],
  [4, 5, 6],
];

arr1.length = 3;
arr2.length = 3;
arr3.length = 5;
array.length = 2; // counts the number of internal array
array[0].length = 3; // first internal array within the outer array

What are the results of these splice and slice methods

✔️ Solution:

var a = ["zero", "one", "two", "three"];
var names = ["jason", "john", "peter", "karen"];

var sliced = a.slice(1, 3);
var spliced = names.splice(1, 3);

// The slice() method returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included). The original array will not be modified.

console.log(sliced); // creates a new array ['one', 'two']
console.log(a); // main array remains untouched

// The splice() method changes the content of an array by removing existing elements and/or adding new elements.

console.log(spliced); // it returns  [ 'john', 'peter', 'karen' ]
console.log(names); // however the array only contains jason now

What are the console logs of these shift and unshift methods

✔️ Solution:

var a = [];

// We take an empty array and

a.unshift(1);
a.unshift(22);
var b = console.log(a);
a.shift();
var c = console.log(a);
a.unshift(3, [4, 5]);
var d = console.log(a);
a.shift();
var e = console.log(a);
a.shift();
var f = console.log(a);
a.shift();
var g = console.log(a);

// Results
var a = [1]; // we a.unshift(1) so added 1 to front

var b = [22, 1]; // we a.unshift(22) so added 22 to front

var c = [1]; // we a.shift() so removed the first element

var d = [3, [4, 5], 1]; // we a.unshift(3,[4,5]) so added these to front
var e = [[4, 5], 1]; // we a.shift() so remove first element

var f = [1]; // we a.shift() so remove first element

var g = []; // we a.shift() so remove first element leaving it empty

Using reduce add all these numbers

var numbers = [1, 2, 3, 4, 5, 6];

✔️ Solution:

var numbers = [1, 2, 3, 4, 5, 6];

var total = numbers.reduce((a, b) => {
  return a + b;
});

console.log(total); // Total returned is : 21

Flatten this array to one single array using reduce

var array = [
  [0, 1],
  [2, 3],
  [4, 5],
];

✔️ Solution:

Var array =  [[0, 1], [2, 3], [4, 5]];

var flattened = array.reduce(function(a, b) {
    return a.concat(b);
},[ ]);

console.log(flattened); // [ 0, 1, 2, 3, 4, 5 ]

Filter this array to return just the dogs

var animals = [
  { name: "Jason", species: "rabbit" },
  { name: "Jessica", species: "dog" },
  { name: "Jacky", species: "owl" },
  { name: "Luke", species: "fish" },
  { name: "Junior", species: "rat" },
  { name: "Thomas", species: "cat" },
];

✔️ Solution:

var animals = [
  { name: "Jason", species: "rabbit" },
  { name: "Jessica", species: "dog" },
  { name: "Jacky", species: "owl" },
  { name: "Luke", species: "fish" },
  { name: "Junior", species: "rat" },
  { name: "Thomas", species: "cat" },
];
Answer;

/******************************************
  filter method with callback function
******************************************/

var dogs = animals.filter(function (animals) {
  return animals.species === "dog";
});

console.log(dogs);

// Returns

[{ name: "Jessica", species: "dog" }];

// The filter() method creates a new array with all elements that pass the test implemented by the provided function.

Using array in question 19 use map function to return all the species

✔️ Solution:

var types = animals.map(function (animals) {
  return animals.species;
});
console.log(types); // [ 'rabbit', 'dog', 'owl', 'fish', 'rat', 'cat' ]

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✅ Solution: Javascript Arrays Interview Questions

Method - #1

Method - #2

Method - #3

Method - #4

Method - #1 (The slice method)

Method - #2 (The for loop method)

✔️ Solution - Method - #1 (The for loop method)

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✅ Solution: Javascript Arrays Interview Questions

Method - #1

Method - #2

Method - #3

Method - #4

Method - #1 (The slice method)

Method - #2 (The for loop method)

✔️ Solution - Method - #1 (The for loop method)

For Example:

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