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HTML

              
                <div id="app"></div>
              
            
!

CSS

              
                $gridSize: 40;
$rowSize: 60;
$cellSize: 15px;
$border: 1px solid #EFEFEF;
$background: #CAEBF2;
$alive: #FF3B3F;
$dead: #A9A9A9;
  
* {
  box-sizing: border-box;
}

body {
  background-color: $background;
  width: 100%;
  height: 100%;
  position: relative;
}

#game-container {
  height: auto;
  width: $rowSize * $cellSize + 40px;
  padding: 10px;
  margin: 30px auto;
  background-color: darken($background, 20%);
  border-radius: 4px;
}
#grid {
  width: $rowSize * $cellSize + 2px;
  height: $gridSize * $cellSize + 2px;
  border: $border;
  margin: 15px auto;
  display: block;
  position: relative;
}

.row {
  width: 100%;
  height: $cellSize;
}
.cell {
  width: $cellSize;
  height: $cellSize;
  display: inline-block;
  border: $border;
}
.alive {
  background-color: $alive;
}
.dead {
  background-color: $dead;
}

h1, h4, h5 {
  font-family: 'Helvetica Neue', Arial, sans-serif;
  font-weight: 300;
  text-align: center;
  margin-bottom: 5px;
}

h5 {
  margin-top: 5px;
}

.menu {
  width: 100%;
  margin: 5px auto 0 auto;
  text-align: center;
  font-family: Helvetica Neue;
  font-weight: 300;
  cursor: pointer;
  
  h3 {
    display: inline-block;
    position: relative;
    font-weight: 300;
    padding: 10px;
    margin: 0;
  }
  button {
    display: inline-block;
    position: relative;
    margin: 0 5px;
    padding: 5px 10px;
    background-color: darken($background, 40%);
    border: none;
    border-radius: 4px;
    &:hover {
      background-color: $background;
    }
  }
  .population {
    background-color: lighten($alive, 20%);
  }
  .active {
    background-color: darken($alive, 20%);
    color: #EFEFEF;
  }
}

#debug {
  position: fixed;
  bottom: 5px;
  left: 5px;
  width: 15px;
  height: 15px;
  content: '';
  border: none;
  background-color: darken($background, 10%);
}
              
            
!

JS

              
                // Components
class BaseComponent extends React.Component {
  _bind(...methods) {
    methods.forEach( (method) => this[method] = this[method].bind(this) );
  }
}

class Cell extends BaseComponent {
  constructor(props) {
    super(props);
    this._bind('handleClick');
  }
  handleClick(e) {
    const target = e.target;
    if (target.className === 'cell dead') {
      // target.className = 'cell alive';
      this.props.onChange('add', e.target.id);
    } else {
      // target.className = 'cell dead';
      this.props.onChange('delete', e.target.id);
    }
  }
  render() {
    const status = this.props.value === 1 ? 'cell alive' : 'cell dead';
    const cellId = `${this.props.row}x${this.props.idx}`;
    return (<div className={status} id={cellId} onClick={this.handleClick}></div>)
  }
}

class Row extends BaseComponent {
  constructor(props) {
    super(props);
    this._bind('handleChange');
  }
  handleChange(type, cell) {
    this.props.onChange(type, cell);
  }
  render() {
    const cells = this.props.cells.map((cell, idx) => <Cell row={this.props.row} value={cell[0]} sum={cell[1]} idx={idx} onChange={this.handleChange} />);
    return (<div className="row">
      {cells}
    </div>);
  }
}
                                     
class Grid extends BaseComponent {
  constructor(props) {
    super(props);
    this._bind('handleChange');
  } 
  handleChange(type, cell) {
    this.props.onChange(type, cell);
  }
  render() {
    const rows = this.props.grid.map((row, idx) => <Row cells={row} row={idx} onChange={this.handleChange}/>);            
    return (<div id="grid">
      {rows}
    </div>)
  }
}

class App extends BaseComponent {
  constructor() {
    super();
    this.state = { 
      grid: [], 
      counter: 0, 
      paused: false, 
      gridSize: 40, 
      rowSize: 60, 
      ratio: 0.7 };
    this._bind(
      'updateState', 
      'buildGrid', 
      'findSums', 
      'applyRules', 
      'start', 
      'stop', 
      'clear', 
      'handleChange', 
      'more', 
      'fewer', 
      'normal', 
      'printout',
    );
  }
  componentWillMount() {
    this.updateState();
  }
  componentDidMount() {
    this.setState({update: false});
  }
  shouldComponentUpdate(nextProps, nextState) {
    if (this.state.update === true) {
      return true;
    }
  }
  updateState() {
    let oldGrid = this.state.grid;
    let newGrid = [];
    let counter = this.state.counter;
    let rows = this.state.gridSize;
    let cells = this.state.rowSize;
    if (counter === 0 && oldGrid.length === 0) {
      newGrid = this.buildGrid(oldGrid, rows, cells);
    } else {
      newGrid = this.applyRules(oldGrid);
    }
    newGrid = this.findSums(newGrid);
    counter++;
    this.setState({ grid: newGrid, counter: counter, update: true});
    this.intervalID = requestAnimationFrame(this.updateState);
  }
  buildGrid(grid, rows, cells) {
    for (let  row = 0; row < rows; row++) {
      grid.push([]);
      for (let cell = 0; cell < cells; cell++) {
        const r = Math.random();
        if(r > this.state.ratio) {
          grid[row].push([1]);
        } else {
          grid[row].push([0]);
        }
      }
    }
    return grid;
  }
  findSums(grid) {
    let newGrid = [];
    grid.forEach((row, rIdx) => {
      let newRow = [];
      row.forEach((cell, cIdx) => {
         let newArr = [];
         newArr.push(cell[0]);
         const neighbourhood = [
          [(rIdx - 1),(cIdx - 1)],
          [(rIdx - 1),(cIdx)],
          [(rIdx - 1),(cIdx + 1)],
          [(rIdx),(cIdx-1)],
          [(rIdx),(cIdx)],
          [(rIdx),(cIdx + 1)],
          [(rIdx + 1),(cIdx - 1)],
          [(rIdx + 1),(cIdx)],
          [(rIdx + 1),(cIdx + 1)]
        ];
        let nValues = neighbourhood.map(arr => {
          let x = arr[0]
          let y = arr[1]
          if (x < 0) {
            x = x + this.state.gridSize;
          } else if (x >= this.state.gridSize) {
            x = x - this.state.gridSize;
          }
          if (arr[0] < 0) {
            
          }
          if (arr[0] < 0 || arr[1] < 0 || arr[0] >= this.state.gridSize || arr[1] >= this.state.rowSize) {
            return 0;
          } else {
            return grid[arr[0]][arr[1]][0];
          }
        });
        let sum = nValues.reduce((sumValues ,n) => sumValues + n);
        newArr.push(sum);
        newRow.push(newArr);
      });
      newGrid.push(newRow);
    });
    return newGrid;
  }
  applyRules(grid) {
    let newGrid = []
    grid.map(row => {
      let newRow = [];
      row.map(cell => {
        const value = cell[0];
        const sum = cell[1];
        if (sum === 3) {
          newRow.push([1]);
        } else if (sum === 4) {
          newRow.push([value]);
        } else {
          newRow.push([0]);
        }
      });
      newGrid.push(newRow);
    });
    return newGrid;
  }
  start() {
    this.setState({ paused: false });
    this.intervalID = requestAnimationFrame(this.updateState);
  }
  stop() {
    cancelAnimationFrame(this.intervalID);
    this.setState({paused: true});
  }
  clear() {
    const grid = this.state.grid;
    if (this.state.paused !== false) {
      cancelAnimationFrame(this.intervalID);
      this.setState({ paused: true });
    }
    let newGrid = [];
    grid.map(row => {
      let newRow = [];
      row.map(cell => newRow.push([0]));
      newGrid.push(newRow);
    });
    this._tempGrid = newGrid;
    this.setState({paused: true, counter: 0, grid: newGrid, update: true});
  }
  handleChange(type, cell) {
    let grid = this.state.grid;
    let arr = cell.split('x');
    if (this.state.paused === true && this.state.counter === 0 && this.state.timer === null) {
      if (type === 'add') {
        grid[arr[0]][arr[1]][0] = 1;
      } else if (type === 'delete') {
        grid[arr[0]][arr[1]][0] = 0;
      }
      let newGrid = this.findSums(grid);
      this.setState({grid: newGrid, update: true});
    } else if (this.state.paused === false) {
      alert('You must pause the simulation and clear the board before you can set up your own.');
    } else if (this.state.counter > 0) {
      alert('You must reset the simulation by pressing "Clear" before you can customize the board.');
    }
  }
  more() {
    cancelAnimationFrame(this.intervalID);
    this.clear();
    this.setState({ ratio: 0.5, grid: [], counter: 0, update: true});
    this.start();
  }
  fewer() {
    cancelAnimationFrame(this.intervalID);
    this.clear();
    this.setState({ ratio: 0.9, grid: [], counter: 0, update: true});
    this.start();
  }
  normal() {
    cancelAnimationFrame(this.intervalID);
    this.clear();
    this.setState({ ratio: 0.7, grid: [], counter: 0, update: true});
    this.start();
  }
  printout() {
    console.log(JSON.stringify(this.state));
  }
  render() { 
    const playPause = this.state.paused === true ? <button id="start" onClick={this.start}><i className="fa fa-play"></i></button> :
      <button id="stop" onClick={this.stop}><i className="fa fa-pause"></i></button>;
    return (<div class="container">
      <h1>Conway's Game of Life</h1>
      <h5><a href="https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life">Click here for an explanation</a></h5>
      <h5>To make your own custom starting state, press clear, click on some squares, and then press Play.</h5>
      <div id="game-container">
        <div className="menu">
          <h3>Generation: {this.state.counter}</h3>
          {playPause}
          <button id="clear" onClick={this.clear}>Clear</button>
        </div><div className="menu">
          <h3 id="restart">Restart with:</h3>
            <button value="0.9" name="population" id="fewer" onClick={this.fewer}>Fewer</button>
          <button value="0.9" name="population" id="fewer" onClick={this.normal}>Normal Amount</button>
          <button value="0.9" name="population" id="fewer" onClick={this.more}>More</button>
        </div>  
        <Grid grid={this.state.grid} onChange={this.handleChange} />
      </div>
        <h4>Coded by <a href="http://lukewalker.org" target="_blank">Luke Walker</a>, to complete <a href="https://www.freecodecamp.com/challenges/build-the-game-of-life" target="_blank">this Free Code Camp project</a>.</h4>
        <button id="debug" onClick={this.printout}></button>
    </div>)
  }
}

ReactDOM.render(<App />, document.querySelector('#app'));


              
            
!
999px

Console