Building a Sudoku Puzzle Game with HTML, CSS, and JavaScript

You know that moment when you start a “quick little project” to brush up on your coding skills, and suddenly you’re three hours deep into Stack Overflow wondering if you’re actually losing your mind? Yeah, that’s how I stumbled into creating a Sudoku puzzle game with HTML, CSS, and JavaScript.

At first, it was just supposed to be a way to stay sharp with JavaScript logic. But now? Now, my friends are like, “Hey, Mr. Sudoku, can you make one where I can save progress?” Save progress?! I’m out here just trying to figure out how to generate a puzzle without breaking the rules.

Anyway, let me walk you through my chaotic, caffeine-fueled adventure of making a Sudoku game from scratch. Spoiler alert: it’s more fun than it sounds, but also significantly harder than I expected.

The Idea: Why Sudoku?

Okay, confession time. I’ve always had this weird respect for Sudoku players. Like, who wakes up and decides, “I’m going to solve a 9×9 grid of numbers for fun today”? It’s such a flex. So, when I was brainstorming ideas for a project, I figured Sudoku would be just complex enough to be interesting, but not so overwhelming that I’d give up halfway through (like my last attempt at building a chess game — RIP).

Plus, Sudoku is pure logic. No guesswork, no random chances. Just strategy. And coding it would mean I’d need to figure out some cool stuff like:

• Creating a grid dynamically with HTML and CSS.
• Using JavaScript to validate inputs and enforce the rules.
• Randomly generating puzzles that are actually solvable.

It sounded doable. Spoiler alert: I underestimated the “actually solvable” part.

Step 1: Building the Grid

First things first, I needed a grid. A glorious 9×9 masterpiece. My approach was to generate it dynamically with JavaScript because hard-coding 81 cells in HTML sounded like a one-way ticket to boredom.

Here’s the basic code I used to whip up the grid:

function createSudokuGrid() {  
    const gridContainer = document.getElementById('sudoku-container');  
    for (let row = 0; row < 9; row++) {  
        const rowDiv = document.createElement('div');  
        rowDiv.classList.add('row');  

        for (let col = 0; col < 9; col++) {  
            const cell = document.createElement('input');  
            cell.type = 'text';  
            cell.maxLength = '1';  
            cell.classList.add('cell');  

            rowDiv.appendChild(cell);  
        }  
        gridContainer.appendChild(rowDiv);  
    }  
}  

createSudokuGrid();  

Boom, we’ve got a grid! 🎉 The CSS for styling it was pretty straightforward—flexbox for the win, obviously:

#sudoku-container {  
    display: grid;  
    grid-template-columns: repeat(9, 1fr);  
    gap: 2px;  
}  
.cell {  
    width: 40px;  
    height: 40px;  
    text-align: center;  
    border: 1px solid #ccc;  
}  

Pro tip: adding subtle borders to separate the 3×3 boxes within the 9×9 grid makes it look way cleaner.

Step 2: Making It Interactive

Now, the fun part. I needed to make the grid actually do something. Specifically, it had to enforce the rules of Sudoku:

1. No duplicates in a row.
2. No duplicates in a column.
3. No duplicates in a 3×3 sub-grid.

Easy, right? (Narrator: It was not easy.)

Here’s how I approached it:

• I added an input event listener to each cell to check for rule violations whenever a number was entered.
• I wrote functions to validate the row, column, and sub-grid based on the cell’s position.

function isValidInput(row, col, value, grid) {  
    // Check row  
    for (let c = 0; c < 9; c++) {  
        if (grid[row][c] === value) return false;  
    }  

    // Check column  
    for (let r = 0; r < 9; r++) {  
        if (grid[r][col] === value) return false;  
    }  

    // Check sub-grid  
    const startRow = Math.floor(row / 3) * 3;  
    const startCol = Math.floor(col / 3) * 3;  
    for (let r = startRow; r < startRow + 3; r++) {  
        for (let c = startCol; c < startCol + 3; c++) {  
            if (grid[r][c] === value) return false;  
        }  
    }  

    return true;  
}  

I won’t lie—debugging this part was a nightmare. At one point, I had numbers disappearing, random errors, and an actual infinite loop situation. But hey, that’s coding, right?

Step 3: Puzzle Generation

This was the real brain-melter. Sudoku puzzles need to be solvable, but generating one randomly is harder than it sounds. I ended up researching a lot (shoutout to every Sudoku algorithm blog ever) and settled on this approach:

1. Start with a solved grid (pre-filled using backtracking).
2. Remove numbers randomly while ensuring the puzzle is still solvable.

Here’s a quick look at the backtracking solver I used:

function solveSudoku(grid) {  
    for (let row = 0; row < 9; row++) {  
        for (let col = 0; col < 9; col++) {  
            if (grid[row][col] === 0) {  
                for (let num = 1; num <= 9; num++) {  
                    if (isValidInput(row, col, num, grid)) {  
                        grid[row][col] = num;  
                        if (solveSudoku(grid)) return true;  
                        grid[row][col] = 0;  
                    }  
                }  
                return false;  
            }  
        }  
    }  
    return true;  
}  

Removing numbers while keeping the puzzle solvable was a delicate balance, but after some trial and error, I managed to get it working.

Step 4: Adding Some Polish

By this point, the game was functional, but it didn’t feel fun. So, I added a few extras:

• A timer to track how long it takes to solve the puzzle.
• A “hint” button that fills in a random cell for you.
• A restart button to clear the grid.

The hint system was surprisingly easy to implement. I just searched for an empty cell, checked its solution, and revealed it to the player.

Final Thoughts

Making this Sudoku game was one of the most satisfying (and frustrating) projects I’ve worked on. It’s crazy how much you learn when you’re solving problems in real time. Plus, now I can say I’ve created something cool that people actually want to play.

If you’re thinking about trying this yourself, go for it! Just stock up on coffee, be ready to Google a lot, and don’t be afraid to experiment.

And hey, if you ever find yourself stuck, hit me up! I may not be a Sudoku master yet, but I’m definitely your guy when it comes to writing code that kinda works. 😅