Arrays are used to store multiple values in a single variable.
Each value is called an element, and each element has a numeric position in the array, known as its index.
Arrays are zero-indexed, meaning the first element is at index 0, the second at index 1, and so on.
Arrays can contain any data type, including numbers, strings, and objects.
const arr1 = [2, 4, 6]; array
arr1[0]; element at index 0 → 2
arr1[1]; element at index 1 → 4
arr1[2]; element at index 2 → 6
arr1[3]; element at index 3 → undefined index not found
Strings are a sequence of zero or more characters written inside quotes used to represent text.
Strings may consist of letters, numbers, symbols, words, or sentences.
Strings are immutable, they cannot be changed.
Each character in a string has an index.
The first character will be index 0 the second character will be index 1 and so on.
There are two ways to access an individual character in a string.
charAt() method
const str1 = "abc"; string
str1.charAt(0); character at index 0 → "a"
str1.charAt(1); character at index 1 → "b"
str1.charAt(2); character at index 2 → "c"
str1.charAt(3); character at index 3 → "" index not found
Alternatively use at() or slice() methods
bracket notation []
const str2 = "abc"; string
str2[0]; character at index 0 → "a"
str2[1]; character at index 1 → "b"
str2[2]; character at index 2 → "c"
str2[3]; character at index 3 → undefined index not found
Numbers are used to represent both integer and floating-point values.
Numbers are most commonly expressed in literal forms like 255 or 3.14159 ↴
let num1 = 5; → number
let num2 = 2.5; → number
let num3 = num1 + num2;
console.log(num3); returns ↴
7.5 → number
Merge two arrays with alternative values using ↴
for loop → executes a block of code a number of times.
push() method → adds specified elements to the end of an array and returns the new length of the array.
Math.max() static method → returns the largest of the numbers given as input parameters, or -Infinity if there are no parameters.
length property → set or return the number of elements in an array.
for loop repeatedly executes a block of code until a specified condition evaluates to false.
The loop runs a block of code a set number of times, defined by an initialization, a condition, and an increment.
for (let x = 0; x < 4; x++) {
console.log(x);
}
Loop variable x is initialized to 0
Condition x < 4 is checked before each iteration.
The loop will continue to run as long as x is less than 4
The loop repeatedly executes a block of code 4 times, from 0 to 3
For each iteration of the loop, the current value of x is printed to the console.
After each iteration, x is incremented by 1 x++
When x reaches 4 the condition evaluates to false, terminating the loop.
0
1
2
3 → printed to console
push() method adds new elements to the end of an array.
Add 4 to end of array.
const arr2 = [1, 2, 3];
arr2.push(4);
console.log(arr2); returns ↴
[1, 2, 3, 4] → 4 added to end of array
The push() method changes the length of the array.
arr2 is modified.
Using the spread operator creates a new array.
Add 4 to a new array.
const arr3 = [1, 2 , 3];
const arr4 = [...arr3, 4];
console.log(arr4); returns ↴
[1, 2, 3, 4] → 4 added to new array
console.log(arr3); returns ↴
[1, 2 ,3]
arr3 remains unchanged.
Math.max() static method returns the largest of the numbers given as input parameters, or -Infinity if there are no parameters.
Directly pass numerical values as arguments.
Math.max(4, 2, 6, 5, 3); returns ↴
6
Use the spread operator to pass an array of numbers.
const arr5 = [4, 2, 6, 5, 3];
Math.max(...arr5); returns ↴
6
length property returns the number of elements in an array.
const arr6 = [1, 2, 3, 4, 5, 6];
arr6.length; returns ↴
6 → there are 6 elements in the array
Initialize variables to hold the two arrays to merge.
const array1 = [1, 3, 5, 7, 9]; → user input
const array2 = [2, 4, 6, 8, 10]; → user input
Define a function alternateMerge to merge two arrays with alternating values.
function alternateMerge(arr1, arr2)
The function takes two arrays as input arr1, arr2 and returns a new array containing the elements of the input arrays merged in alternating value. The original arrays are unchanged.
Initialize an empty array to hold the merged result.
const mergedArray = [] mergedArray
The input arrays may be of different lengths.
Determine the maximum length of the two arrays to ensure that the loop iterates the correct number of times.
const maxLength = Math.max(arr1.length, arr2.length) maxLength
Loop through the maximum length maxLength of the two arrays.
for (let x = 0; x < maxLength; x++) {}
If the current index x is within the bounds of arr1 push the element arr1[x] to mergedArray
if (x < arr1.length) mergedArray.push(arr1[x])
If the current index x is within the bounds of arr2 push the element arr2[x] to mergedArray
if (x < arr2.length) mergedArray.push(arr2[x])
Return the merged array.
return mergedArray
Merge two arrays.
const array1 = [1, 3, 5, 7, 9];
const array2 = [2, 4, 6, 8, 10];
function alternateMerge(arr1, arr2) {
const mergedArray = [];
const maxLength = Math.max(arr1.length, arr2.length);
for (let x = 0; x < maxLength; x++) {
if (x < arr1.length) mergedArray.push(arr1[x]);
if (x < arr2.length) mergedArray.push(arr2[x]);
}
return mergedArray;
}
call function
alternateMerge(array1, array2); returns ↴
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]