JavaScript/Arrays/Exercises

Topic: Arrays

1. What is the output of the following script?

"use strict";

const x = [];
x[1] = 5;
console.log(x);

x[2] = [, , 42];
console.log(x);

Click to see solution

[undefined, 5]
[undefined, 5, [undefined, undefined, 42]]

2. Add elements

Create an array with all odd numbers that are smaller than 10.
Show the array with the alert command.
Show how many elements the array contains.
Add 2, 4, 6, 8 to the end of the array and show it again.
Insert the value 20 on the 20th array element and show the array again.

Click to see solution

"use strict";

// literal notation
const arr = [1, 3, 5, 7, 9];
alert(arr);  // or: console.log(arr);

alert("The array contains " + arr.length + " elements.");

// add elements
arr.push(2, 4, 6, 8);
alert(arr);

// one certain element
arr[19] = 20;    // 19!
alert(arr);
alert("The array now contains " + arr.length + " elements.");

3. Remove elements

Create an array with all numbers from 1 to 6.
Show the array with the alert command.
Delete the first and last element and show the resulting array.

Click to see solution

"use strict";
const arr = [1, 2, 3, 4, 5, 6];
alert(arr);  // or: console.log(arr);

// remove elements
const first = arr.shift();
alert("Removed the first element: " + first);
alert(arr);

const last = arr.pop();
alert("Removed the last element: " + last);
alert(arr);

4. Combine elements

Create an empty array.
Add 0, 1, 2 to the array with the push method and show the array.
Create the string "0 + 1 + 2" out of the array using the join method and show the string.

Click to see solution

"use strict";

const arr = [];
arr.push(0);
arr.push(1);
arr.push(2);
alert(arr);

const str = arr.join(" + ");
alert(str);