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

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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

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Generate a fibonacci sequence up to n terms using ↴

while loop → repeatedly executes a block of code as long as a specified condition is true.

slice() method → returns selected elements in an array, as a new array.

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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

}

const arr = []; → empty array

let x = 0; → counter

while (x < 4) {

arr.push(x);

x++;

}

console.log(arr);

Initialize an empty array arr outside of the loop.

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 pushed to the end of the array.

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] → array returned

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slice() method returns selected elements in an array, as a new array.

syntax ↴

slice(start) return a new array from start index to end of array

slice(start, end) return an array from start index to end index of array (exclusive).

Return a new array from index 1 to end of array.

const arr2 = [1, 2, 3, 4];

arr2.slice(1); start index is 1

returns ↴

[2, 3, 4]

Return a new array from index 1 to index 4 (exclusive).

const arr3 = [1, 2, 3, 4];

arr3.slice(1, 3); start index is 1 end index is 4 (not included)

returns ↴

[2, 3]

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Initialize a variable to hold number of terms n to generate for a Fibonacci sequence.

const nTerms = n; → user input

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Define a function fibonacci() to generate a Fibonacci sequence.

function fibonacci(num) {}

The function takes a number as input num and generates first n terms of the Fibonacci sequence.

Initialize the array with the first two Fibonacci numbers 0 and 1

let fib = [0, 1] fib

Start from the third term.

let x = 2 x

Loop while x is less than num

while (x < num) {}

Each term is the sum of the two preceding terms.

fib[x] = fib[x - 1] + fib[x - 2]

Increment the index by 1

x++

Return the array fib sliced to the number of terms num requested.

return fib.slice(0, num)

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Call the function with ↴

fibonacci(nTerms);

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Generate the first 7 terms of the Fibonacci sequence.

The current Fibonacci number is computed by adding the two previous numbers in the array.

fib = [0, 1] array initialized with the first two numbers of the series.

fib[0] first number   0 [0, 1]

fib[1] second number   1 [0, 1]

Loop to calculate the Fibonacci numbers from the 3rd term onward.

let x = 2

while (x < num) {}

Add number at index [x - 1] to number at index [x - 2]

fib[x] = fib[x - 1] + fib[x - 2]

First 7 terms of the Fibonacci sequence ↴

[0, 1, 1, 2, 3, 5, 8]

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Generate the first 7 terms of the Fibonacci sequence.

const nTerms = 7;

function fibonacci(num) {

let fib = [0, 1];

let x = 2;

while (x < num) {

fib[x] = fib[x - 1] + fib[x - 2];

x++;

}

return fib.slice(0, num);

}

call function

fibonacci(nTerms); returns ↴

[0, 1, 1, 2, 3, 5, 8]