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 ↴
while loop → repeatedly executes a block of code as long as a specified condition is true.
push() method → adds specified elements to the end of an array and returns the new length of the array.
length property → set or return the number of elements in an array.
while loop repeatedly executes a block of code as long as a specified condition evaluates to true.
while (condition) {
// execute code as long as condition is true
}
let x = 0; → counter
while (x < 4) {
console.log(x);
x++;
}
Initialize a counter variable x outside of the loop.
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.
length property returns the number of elements in an array.
const arr5 = [1, 2, 3, 4, 5, 6];
arr5.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 into a new array 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
Initialize an index variable to track the current position in both arrays.
let x = 0 x
A while loop iterates through the indices of both arrays, checking their lengths to ensure all elements are processed.
Loop until all elements from both arrays are processed.
while (x < arr1.length || x < arr2.length) {}
If there are elements left in arr1 add the current element arr1[x] to mergedArray
if (x < arr1.length)
mergedArray.push(arr1[x])
If there are elements left in arr2 add the current element arr2[x] to mergedArray
if (x < arr2.length)
mergedArray.push(arr2[x])
Increment the index for the next iteration.
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 = [];
let x = 0;
while (x < arr1.length || x < arr2.length) {
if (x < arr1.length) {
mergedArray.push(arr1[x]);
}
if (x < arr2.length) {
mergedArray.push(arr2[x]);
}
x++;
}
return mergedArray;
}
call function
alternateMerge(array1, array2); returns ↴
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]