Common array operations in Javascript - Step-by-Step Execution

Concept Flow - Common array operations

Start with an array

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Access elements by index

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Add elements (push/pop, unshift/shift)

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Modify elements

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Search elements (indexOf, includes)

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Iterate over elements (forEach, map)

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End of operations

This flow shows how we start with an array and perform common operations like accessing, adding, modifying, searching, and iterating elements.

Execution Sample

Javascript

const arr = [10, 20, 30];
arr.push(40);
const first = arr[0];
arr[1] = 25;
const has30 = arr.includes(30);
arr.forEach(x => console.log(x));

This code creates an array, adds an element, accesses and modifies elements, checks for a value, and prints all elements.

Execution Table

Step	Operation	Array State	Variables Changed	Output/Notes
1	Initialize arr	[10, 20, 30]	arr	Array created with 3 elements
2	arr.push(40)	[10, 20, 30, 40]	arr	40 added at the end
3	Access arr[0]	[10, 20, 30, 40]	first = 10	first stores 10
4	Modify arr[1] = 25	[10, 25, 30, 40]	arr	Second element changed from 20 to 25
5	Check arr.includes(30)	[10, 25, 30, 40]	has30 = true	30 is found in array
6	arr.forEach(x => console.log(x))	[10, 25, 30, 40]	-	Prints 10, 25, 30, 40 each on new line
7	End	[10, 25, 30, 40]	arr, first, has30	All operations done

💡 All common array operations executed step-by-step

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	Final
arr	[10, 20, 30]	[10, 20, 30, 40]	[10, 20, 30, 40]	[10, 25, 30, 40]	[10, 25, 30, 40]	[10, 25, 30, 40]	[10, 25, 30, 40]
first	undefined	undefined	10	10	10	10	10
has30	undefined	undefined	undefined	undefined	true	true	true

Key Moments - 3 Insights

Why does arr.push(40) add the element at the end and not the beginning?

arr.push() always adds elements to the end of the array, unlike arr.unshift() which adds to the beginning. This is shown in execution_table step 2 where 40 is appended.

Why does modifying arr[1] change the second element and not the first?

Array indexes start at 0, so arr[1] refers to the second element. Step 4 in execution_table shows arr[1] changed from 20 to 25.

What does arr.includes(30) return if 30 is not in the array?

arr.includes(value) returns false if the value is not found. In step 5, it returns true because 30 is present.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the value of variable 'first'?

A 10

B 20

C 30

D undefined

💡 Hint

Check the 'Variables Changed' column at step 3 in execution_table

At which step does the array change from [10, 20, 30] to [10, 25, 30, 40]?

A Step 2

B Step 5

C Step 4

D Step 6

💡 Hint

Look at the 'Array State' column in execution_table for each step

If we replaced arr.push(40) with arr.unshift(40), what would be the array state after step 2?

A [10, 20, 30, 40]

B [40, 10, 20, 30]

C [10, 20, 30]

D [40]

💡 Hint

unshift adds element to the start of the array, check step 2 array state for push

Concept Snapshot

Common array operations in JavaScript:
- Access elements by index: arr[0]
- Add elements: push() adds at end, unshift() at start
- Remove elements: pop() removes last, shift() removes first
- Modify elements by index
- Search with includes() or indexOf()
- Iterate with forEach() or map()

Full Transcript

This lesson shows common array operations in JavaScript. We start with an array of numbers. We add a new number at the end using push. We access the first element by index 0 and store it in a variable. We modify the second element by assigning a new value. We check if a number exists in the array using includes. Finally, we print all elements using forEach. The execution table tracks each step, showing how the array and variables change. Key moments clarify why push adds at the end, how indexing works, and what includes returns. The quiz tests understanding of variable values and array states during execution.