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HTML

              
                <div id="root" />

<!--
PROJECT NOTE:
- Started effective on Nov 14, 2021, and completed on Nov 17, 2021.
- I thought this project would be simple and straightforward. Boy I was wrong. setInterval and setTimeout don't get along very well with React's state tracking character.
- Biggest challenge in this project is to be able to clearInterval. Just a mere clearInterval won't suffice the activated setInterval. We need to have a tracker in the state, whether a setInterval is active or not. Next difficult is to guess what the test specs expected. The test really expected to see that timer hit 00:00 before alarm beeped on and session turned into break v.v. (the resolve is to set them to set off at -1000 instead of 0). It also wanted to see a synchronized timing between pause time and replay time. I don't think I would know that if I didn't search past questions in the forum. Hypothetically, my chaining the beep.play, this.setState(()=>), and clearInterval() SERIALLY, causing the different timestamps between the alarm sound started to play, the (left)state.duration captured, and the clearing of setInterval (as much as 2 seconds). This flaw was resolved by moving all of them inside the this.setState(()=>) callback function so that the state updating and the invocation of all required functions were done at once, thus they’re synchronized.


- I am happy with the design utilizing state[false] and state[true], that I don't have to track the state, just whenever time reached 0. It'll just replay "the other side of the coin", using !(bang operator) for changing the mode. When the mode value is change, then this.state[mode] I set up for the values will also change just by accessing the index 0 and index 1 for the corresponding parameter in the render method.
- This code may be refactored to look sleek, using ternary in replace of the if-else conditional statement.
- I am excited that this app passed the test specs whenever wherever.
- It's MVP and with some cleanups easily 'shippable', IMO.

Question asked & note added:
- https://forum.freecodecamp.org/t/25-5-clock-cant-read-properties-of-null-timer-hasnt-reached-0/485679/2

Reference:
- model: https://codepen.io/freeCodeCamp/full/XpKrrW
- reading that enabled me to start creating the skeleton: https://www.educative.io/edpresso/how-to-create-a-countdown-timer-using-javascript
- dynamic setInterval. Read for logic, but useInterval not applied. https://overreacted.io/making-setinterval-declarative-with-react-hooks/
- Seen but not referred to for this project: https://codepen.io/Malik_Mortis/pen/abJOmLg?editors=0011
- Switch must fired only when duration = -1000 : https://forum.freecodecamp.org/t/25-5-clock-help-expected-0-to-be-above-0-solved-sorta/459433
- audio play (on switch) and rewind (on reset): https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Video_and_audio_APIs
- other audio: https://coderrocketfuel.com/article/how-to-play-a-mp3-sound-file-in-react-js
- forcing two digits display for the clock with toLocaleString: https://stackoverflow.com/questions/8043026/how-to-format-numbers-by-prepending-0-to-single-digit-numbers/8043056
-->
              
            
!

CSS

              
                body {
  background: linear-gradient(0.75turn, #3f87a6, #ebf8e1, #f69d3c);
}

#root {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-self: center;
  margin-top: 10%;
}

#container {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 1em;
}

#break-container {
  display: grid;
  grid-template-areas:
    "break-label break-label break-label"
    "down break-length up";
}

#break-label {
  grid-area: break-label
}

#settings {
  display: flex;
  flex-direction: row;
  gap: 1.8em;
}

#break-length,
#session-length {
  text-align: center;
}

#session-container {
  display: grid;
  grid-template-areas:
    "session-label session-label session-label"
    "down session-length up";
}

#session-label {
  grid-area: session-label
}

#timer-container {
  border: 1px solid gray;
  border-radius: .3em;
  padding-left: 2em;
  padding-right: 2em;
  padding-bottom: 1em;
  display: flex;
  flex-direction: column;
}

#time-left {
  display: flex;
  justify-content: space-around;
}

#todo {
  display: flex;
  gap: 1em;
}

#footer {
  margin-top: 2em;
  font-size: .7em;
  text-align: center;
}
              
            
!

JS

              
                
class Clock255 extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      "false": ["Break", 5], 
      "true": ["Session", 25],
      mode: true,
      duration: 25 * 60 * 1000, // in min.
      intervalId: 0,
    }
    this.increment = this.increment.bind(this);
    this.decrement = this.decrement.bind(this);
    this.reset = this.reset.bind(this);
    this.play = this.play.bind(this);
    this.switch = this.switch.bind(this)
  }
  
  // this function handle the start/stop timer button
  play = () => {
    if (this.state.intervalId) {
      clearInterval(this.state.intervalId);
      this.setState((state) => {
        let newDuration = state.duration;
        return {
          ...state,
          duration: newDuration,
          // duration: newDuration + 2000(ms) always pass the first test run, not the subsequent ones
          intervalId: 0,
        };
      });
      return;
    }

    const newIntervalId = setInterval(() => {
      this.setState((state) => {
        let newDuration = state.duration - 1000;
        // if duration = 0, we invoke switch()
        if (newDuration === -1000) {
          // -1000 to let test spec see 00:00 for 1 sec.
          return this.switch();
        } 
        else {
          return {
            ...state,
            duration: newDuration
          };          
        }
      });
    }, 1000);
    
    this.setState((state) => {
      return {
        ...state,
        intervalId: newIntervalId,
      };
    });
    
/*    const setTimeoutID = setTimeout(this.switch, this.state.duration + 900);
      is removed and replaced with a 'listener' in newIntervalId, if duration
      is -1000, invoke switch. We can't have setTimeout as it works outside of
      this.state, thus they might conflicting each other.
*/
    
  }

  /* FLAWED METHOD. Replaced. See remarks below.
  switch() {
    const currentState = {...this.state};
    const newMode = !currentState.mode;
    const beep = document.getElementById("beep");
      beep.play();
      let resetState = {
        "false": [...currentState["false"]], 
        "true": [...currentState["true"]],
        mode: newMode,
        duration: currentState[newMode][1] * 60 * 1000,
        intervalId: 0
      };
      clearInterval(this.state.intervalId);
      this.setState(resetState);
      return this.play();
    }
    
    This method is flawed, thus replaced with the one below.
    If we put beep.play() and clearInterval outside of this.setState,
    it became a chained process, thus, a lag for a couple ms. should
    be expected between one invocation and the others, causing them
    to not completely synchronized. When we put everything inside of
    this.setState, they all became synchronized because they all got
    invoked together with the state updating at once (in parallel to
    each other)
    */

  switch() {
    const currentState = {...this.state};
    const newMode = !currentState.mode;
    const beep = document.getElementById("beep");
    this.setState((state) => {
      beep.play();
      clearInterval(state.intervalId);
      state.mode = newMode;
      state.duration = currentState[newMode][1] * 60 * 1000;
      state.intervalId = 0;
      this.play();
      return;
    })
  }
  
  increment(event) {
    this.setState((state) => {
      if (event.target.id === "break-increment" && state["false"][1] < 60) {
        if (state.mode === false && state.intervalId === 0) {
          let newFalse = [...state["false"]];
          newFalse[1] += 1;
          state["false"] = newFalse;
          state.duration = state["false"][1] * 60 * 1000; 
          return state;      
        }
        else if (state.mode === true) {
          let newFalse = [...state["false"]];
          newFalse[1] += 1;
          state["false"] = newFalse;      
          return state;                
        }
      } 
      else if (event.target.id ==="session-increment" && state["true"][1] < 60) {
        if (state.mode === true && state.intervalId === 0) {
          let newTrue = [...state["true"]];
          newTrue[1] += 1;
          state["true"] = newTrue;
          state.duration = state["true"][1] * 60 * 1000;
          return state;
        }
        else if (state.mode === false && state.intervalId === 0) {
          let newTrue = [...state["true"]];
          newTrue[1] += 1;
          state["true"] = newTrue;
          return state;
        }
      }
      else {
        return;
      }
    })
  }
  
  decrement(event) {
    this.setState((state) => {
      if (event.target.id === "break-decrement" && state["false"][1] > 1) {
        if (state.mode === false && state.intervalId === 0) {
          let newFalse = [...state["false"]];
          newFalse[1] -= 1;
          state["false"] = newFalse;
          state.duration = state["false"][1] * 60 * 1000;       
          return state;      
        }
        else if (state.mode === true) {
          let newFalse = [...state["false"]];
          newFalse[1] -= 1;
          state["false"] = newFalse;      
          return state;                
        }
      } 
      else if (event.target.id ==="session-decrement" && state["true"][1] > 1) {
        if (state.mode === true && state.intervalId === 0) {
          let newTrue = [...state["true"]];
          newTrue[1] -= 1;
          state["true"] = newTrue;
          state.duration = state["true"][1] * 60 * 1000;
          return state;
        }
        else if (state.mode === false && state.intervalId === 0) {
          let newTrue = [...state["true"]];
          newTrue[1] -= 1;
          state["true"] = newTrue;
          return state;
        }
      }
      else {
        return;
      }
    })
  }
  
  reset = () => {
    const beep = document.getElementById("beep");
    beep.pause();
    beep.currentTime = 0;
    clearInterval(this.state.intervalId);
    if (this.state.intervalId && this.state.duration === 0) {
      this.setState((state) => {
        return {
          "false": ["Break", 5], 
          "true": ["Session", 25],
          mode: true,
          duration: 25 * 60 * 1000,
          intervalId: 0          
        }
      })
    }
    else {
      this.setState((state) => {
        return {
          "false": ["Break", 5], 
          "true": ["Session", 25],
          mode: true,
          duration: 25 * 60 * 1000,
          intervalId: 0          
        }
      })
    }
  }
        
  render() {
    // console.log("mode: " + this.state.mode, "duration: " + this.state.duration / 1000, );
    return (
      <div id="root">
        <div id="audio">
          <audio id="beep" src="https://raw.githubusercontent.com/freeCodeCamp/cdn/master/build/testable-projects-fcc/audio/BeepSound.wav"></audio>
        </div>
        <div id="container">
          <h1 id="title">25 + 5 Clock</h1>
          <div id="settings">
            <section id="break-container">
              <h2 id="break-label">Break Length</h2>
              <button id="break-decrement" onClick={this.decrement}>down</button>
              <div id="break-length">{this.state["false"][1]}</div>
              <button id="break-increment" onClick={this.increment}>up</button>
            </section>
            <section id="session-container">
              <h2 id="session-label">Session Length</h2>
              <button id="session-decrement" onClick={this.decrement}>down</button>
              <div id="session-length">{this.state["true"][1]}</div>
              <button id="session-increment" onClick={this.increment}>up</button>
            </section>
          </div>
          <section id="timer-container">
            <h2 id="timer-label">{this.state[this.state.mode][0]}</h2>
            <div id="time-left">
                {Math.floor(this.state.duration / (1000 * 60)).toLocaleString('en-US', {
    minimumIntegerDigits: 2,
    useGrouping: false
  })}
              : 
                {Math.floor((this.state.duration % (1000 * 60)) / 1000).toLocaleString('en-US', {
    minimumIntegerDigits: 2,
    useGrouping: false
  })}
            </div>
          </section>
          <section id="todo">
            <button id="start_stop" onClick={this.play}>{this.state.intervalId ? "stop" : "start"}</button>
            <button id="reset" onClick={this.reset}>reset</button>
          </section>
        </div>
        <p id="footer">Shugyoza, 2021, with React based on <a href="https://www.freecodecamp.org/learn/front-end-development-libraries/front-end-development-libraries-projects/build-a-25--5-clock" target="_blank">User Stories</a> and <a href="https://codepen.io/freeCodeCamp/full/XpKrrW" target="_blank">Model</a></p>
      </div>
    )
  }
}

ReactDOM.render(<Clock255 />, document.getElementById("root"));


// !! IMPORTANT README:

// You may add additional external JS and CSS as needed to complete the project, however the current external resource MUST remain in place for the tests to work. BABEL must also be left in place. 

/***********
INSTRUCTIONS:
  - Select the project you would 
    like to complete from the dropdown 
    menu.
  - Click the "RUN TESTS" button to
    run the tests against the blank 
    pen.
  - Click the "TESTS" button to see 
    the individual test cases. 
    (should all be failing at first)
  - Start coding! As you fulfill each
    test case, you will see them go   
    from red to green.
  - As you start to build out your 
    project, when tests are failing, 
    you should get helpful errors 
    along the way!
    ************/

// PLEASE NOTE: Adding global style rules using the * selector, or by adding rules to body {..} or html {..}, or to all elements within body or html, i.e. h1 {..}, has the potential to pollute the test suite's CSS. Try adding: * { color: red }, for a quick example!

// Once you have read the above messages, you can delete all comments. 

/*
Play and tick only works to the extend of starting countdown, but unable to stop/reset
  
//   play() {
//     let dt = new Date();
//     let future = d.setMinutes(dt.getMinutes() + this.state[this.state.session][1]);
//     this.tick(future);
//   }
  
//   tick(future) {
//     setInterval(() => {
//       let distance = future - Date.now();
//       let minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
//       let seconds = Math.floor((distance % (1000 * 60)) / 1000);
//       this.setState((state) => {
//         return state.display = [minutes, seconds]
//       })
//     }, 1000);
//   }
  
  // timeLeft(future) {
  //   let distance = future - Date.now();
  //   let minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
  //   let seconds = Math.floor((distance % (1000 * 60)) / 1000);
  //   this.setState((state) => {
  //     state.display = [minutes, seconds]
  //   })
  // }
*/
              
            
!
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