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Connect 4 | Javascript

Hi everyone. In today’s tutorial, we will learn how to create connect 4 game. To create this game, we need HTML, CSS and JavaScript.

In this game, we assign each player a few discs. The goal of this game is to drop the discs into empty spaces. Next the players have to connect any four discs vertically, horizontally or diagonally. The first player to do this wins. This is a two-player game. If all the empty spaces are filled without anyone connecting any discs then the game is considered to be over.

This is an expert-level JavaScript game. I would recommend beginners to try beginner-level projects before trying this one. If you are looking for more such projects to improve your JavaScript skills, you can check out this playlist here. This playlist contains 100 + JavaScript projects that will help you improve your JavaScript skills.

Video Tutorial:

If you are interested to learn by watching a video tutorial instead of reading this blog post, you can check out the video down below. Also, subscribe to my YouTube channel, where I post new tips, tricks and tutorials every alternate day.
 

Project Folder Structure:

Before we start coding, let us take a look at the project folder structure. Which theatre project folder is called connect 4. Inside this folder, we have 3 files. These files are index.html, style.css and script.js. The first file is the HTML document second one is the style sheet, and finally, we have the script file.

HTML:

We begin with the HTML file. Copy the code below and paste it into your HTML document.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Connect 4</title>
    <!-- Google Fonts -->
    <link
      href="https://fonts.googleapis.com/css2?family=Poppins:wght@400;500&display=swap"
      rel="stylesheet"
    />
    <!-- Stylesheet -->
    <link rel="stylesheet" href="style.css" />
  </head>
  <body>
    <div class="wrapper">
      <div id="playerTurn">Demo Text</div>
      <div class="container"></div>
      <div id="information">
        <div class="player-wrappers">
          Player 1
          <div class="player1"></div>
        </div>
        <div class="player-wrappers">
          Player 2
          <div class="player2"></div>
        </div>
      </div>
    </div>
    <div class="startScreen">
      <div id="message"></div>
      <button id="start">Start Game</button>
    </div>
    <!-- Script -->
    <script src="script.js"></script>
  </body>
</html>

CSS:

Next phase style this game using CSS. For this copy, the code provided to you below and paste it into your style sheet.

body {
  margin: 0;
  padding: 0;
  font-family: "Poppins", sans-serif;
  background-color: #416cea;
}
.wrapper {
  width: 33.75em;
  background-color: #ffffff;
  position: absolute;
  padding: 2em;
  transform: translateX(-50%);
  left: 50%;
  top: 1.25em;
  border-radius: 0.5em;
}
.container {
  margin: 1.25em auto;
  width: 33.75em;
  border-radius: 0.6em;
  overflow: hidden;
  background-color: #416cea;
}
#information {
  display: grid;
  width: 100%;
  grid-template-columns: 1fr 1fr;
}
.player-wrappers {
  display: flex;
  align-items: center;
  flex-direction: column;
}
.player1:before {
  content: "";
  display: inline-block;
  width: 3.12em;
  height: 3.12em;
  border-radius: 50%;
  background: radial-gradient(#fff04e 1.12em, #ffc400 1.25em);
}
.player2:before {
  content: "";
  display: inline-block;
  width: 3.12em;
  height: 3.12em;
  border-radius: 50%;
  background: radial-gradient(#ff4747 1.12em, #c00303 1.25em);
}
#playerTurn {
  margin: 1em 0;
  text-align: right;
}
#playerTurn span {
  font-weight: 600;
}
.startScreen {
  position: absolute;
  top: 0;
  height: 100vh;
  width: 100vw;
  background-color: #416cea;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}
.startScreen button {
  background-color: #ffffff;
  font-size: 1.4em;
  padding: 1em 2em;
  border: none;
  outline: none;
  border-radius: 2em;
  cursor: pointer;
}
.grid-row {
  margin: 0 auto;
  display: flex;
}
.grid-box {
  width: 5em;
  height: 5em;
  display: grid;
  place-items: center;
  background: radial-gradient(white 1.37em, #416cea 1.43em);
  cursor: pointer;
}
.hide {
  display: none;
}
#message {
  margin-bottom: 1em;
  color: #ffffff;
  font-size: 1.2em;
}

Javascript:

Next, we implement the logic and functionality for this game using simple steps. We do so by using JavaScript. Now copy the code below and paste it into a script file.
//Initial references
const container = document.querySelector(".container");
const playerTurn = document.getElementById("playerTurn");
const startScreen = document.querySelector(".startScreen");
const startButton = document.getElementById("start");
const message = document.getElementById("message");
let initialMatrix = [
  [0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0],
];
let currentPlayer;

//Random Number Between Range
const generateRandomNumber = (min, max) =>
  Math.floor(Math.random() * (max - min)) + min;

//Loop through array and check for same values
const verifyArray = (arrayElement) => {
  let bool = false;
  let elementCount = 0;
  arrayElement.forEach((element, index) => {
    if (element == currentPlayer) {
      elementCount += 1;
      if (elementCount == 4) {
        bool = true;
      }
    } else {
      elementCount = 0;
    }
  });
  return bool;
};

//Check for game over(Last step)
const gameOverCheck = () => {
  let truthCounnt = 0;
  for (let innerArray of initialMatrix) {
    if (innerArray.every((val) => val != 0)) {
      truthCounnt += 1;
    } else {
      return false;
    }
  }
  if (truthCounnt == 6) {
    message.innerText = "Game Over";
    startScreen.classList.remove("hide");
  }
};

//Check rows
const checkAdjacentRowValues = (row) => {
  return verifyArray(initialMatrix[row]);
};

//Check columns
const checkAdjacentColumnValues = (column) => {
  let colWinCount = 0,
    colWinBool = false;
  initialMatrix.forEach((element, index) => {
    if (element[column] == currentPlayer) {
      colWinCount += 1;
      if (colWinCount == 4) {
        colWinBool = true;
      }
    } else {
      colWinCount = 0;
    }
  });
  //no match
  return colWinBool;
};

//Get Right diagonal values
const getRightDiagonal = (row, column, rowLength, columnLength) => {
  let rowCount = row;
  let columnCount = column;
  let rightDiagonal = [];
  while (rowCount > 0) {
    if (columnCount >= columnLength - 1) {
      break;
    }
    rowCount -= 1;
    columnCount += 1;
    rightDiagonal.unshift(initialMatrix[rowCount][columnCount]);
  }
  rowCount = row;
  columnCount = column;
  while (rowCount < rowLength) {
    if (columnCount < 0) {
      break;
    }
    rightDiagonal.push(initialMatrix[rowCount][columnCount]);
    rowCount += 1;
    columnCount -= 1;
  }
  return rightDiagonal;
};

const getLeftDiagonal = (row, column, rowLength, columnLength) => {
  let rowCount = row;
  let columnCount = column;
  let leftDiagonal = [];
  while (rowCount > 0) {
    if (columnCount <= 0) {
      break;
    }
    rowCount -= 1;
    columnCount -= 1;
    leftDiagonal.unshift(initialMatrix[rowCount][columnCount]);
  }
  rowCount = row;
  columnCount = column;
  while (rowCount < rowLength) {
    if (columnCount >= columnLength) {
      break;
    }
    leftDiagonal.push(initialMatrix[rowCount][columnCount]);
    rowCount += 1;
    columnCount += 1;
  }
  return leftDiagonal;
};

//Check diagonal
const checkAdjacentDiagonalValues = (row, column) => {
  let diagWinBool = false;
  let tempChecks = {
    leftTop: [],
    rightTop: [],
  };
  let columnLength = initialMatrix[row].length;
  let rowLength = initialMatrix.length;

  //Store left and right diagonal array
  tempChecks.leftTop = [
    ...getLeftDiagonal(row, column, rowLength, columnLength),
  ];

  tempChecks.rightTop = [
    ...getRightDiagonal(row, column, rowLength, columnLength),
  ];
  //check both arrays for similarities
  diagWinBool = verifyArray(tempChecks.rightTop);
  if (!diagWinBool) {
    diagWinBool = verifyArray(tempChecks.leftTop);
  }
  return diagWinBool;
};

//Win check logic
const winCheck = (row, column) => {
  //if any of the functions return true we return true
  return checkAdjacentRowValues(row)
    ? true
    : checkAdjacentColumnValues(column)
    ? true
    : checkAdjacentDiagonalValues(row, column)
    ? true
    : false;
};

//Sets the circle to exact points
const setPiece = (startCount, colValue) => {
  let rows = document.querySelectorAll(".grid-row");
  //Initially it will place the circles in the last row else if no place availabke we will decrement the count until we find empty slot
  if (initialMatrix[startCount][colValue] != 0) {
    startCount -= 1;
    setPiece(startCount, colValue);
  } else {
    //place circle
    let currentRow = rows[startCount].querySelectorAll(".grid-box");
    currentRow[colValue].classList.add("filled", `player${currentPlayer}`);
    //Update Matrix
    initialMatrix[startCount][colValue] = currentPlayer;
    //Check for wins
    if (winCheck(startCount, colValue)) {
      message.innerHTML = `Player<span> ${currentPlayer}</span> wins`;
      startScreen.classList.remove("hide");
      return false;
    }
  }
  //Check if all are full
  gameOverCheck();
};

//When user clicks on a box
const fillBox = (e) => {
  //get column value
  let colValue = parseInt(e.target.getAttribute("data-value"));
  //5 because we have 6 rows (0-5)
  setPiece(5, colValue);
  currentPlayer = currentPlayer == 1 ? 2 : 1;

  playerTurn.innerHTML = `Player <span>${currentPlayer}'s</span> turn`;
};

//Create Matrix
const matrixCreator = () => {
  for (let innerArray in initialMatrix) {
    let outerDiv = document.createElement("div");
    outerDiv.classList.add("grid-row");
    outerDiv.setAttribute("data-value", innerArray);
    for (let j in initialMatrix[innerArray]) {
      //Set all matrix values to 0
      initialMatrix[innerArray][j] = [0];
      let innerDiv = document.createElement("div");
      innerDiv.classList.add("grid-box");
      innerDiv.setAttribute("data-value", j);
      innerDiv.addEventListener("click", (e) => {
        fillBox(e);
      });
      outerDiv.appendChild(innerDiv);
    }
    container.appendChild(outerDiv);
  }
};

//Initialise game
window.onload = startGame = async () => {
  //Between 1 and 2
  currentPlayer = generateRandomNumber(1, 3);
  container.innerHTML = "";
  await matrixCreator();
  playerTurn.innerHTML = `Player <span>${currentPlayer}'s</span> turn`;
};

//start game
startButton.addEventListener("click", () => {
  startScreen.classList.add("hide");
  startGame();
});

 
That’s it for this project. If you face any issues while creating this project, you can download the source code by clicking on the download button below. Also, if you have any query suggestions or feedback, you can comment on them below.
Happy coding
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