This project is all about Asynchronous Programming.
Final Project in Front-end Libraries, freeCodeCamp
The challenge of this project is how to handle the async programming that is required, since we are dealing with a clock that can reset, update session, update break and wait for 1 second till the next state update.
You can think of Async Programming like things happening at the same time, one thing can get longer than another, but the program will run normally, it will not stop to await one process that takes time, but this process when resolved or rejected will notify the program to use it's promised result. Since async programming is about handle processes that takes time, it is directly related to promises, a promise is a process that its result will be available in some point in the future. A good example that I use in my mind to think about asynchronicity is cooking, if you must prepare a juice and a steak you have two approaches:
-
1, put the steak in the pan, await 4 minutes so it gets prepared (the steak can get two results, a good steak or a bad steak) and then make the juice.
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2, put the steak in the pan, make the juice while the steak is getting prepared, finish the juice and handle the result of the steak, a good or a bad result.
The second approach is async (and faster)! You're doing more than one thing at a time.
An example of asynchronous programming is the following code:
const startRun = () => {
setTimeoutRef(
setTimeout(() => {
updateTimeLeft()
}, 1000)
)
}
React.useEffect(() => {
if (clock.running) startRun()
else clearTimeout(timeoutRef)
}, [clock.running, clock.timeLeft])
const handleRun = () => {
toggleRunning()
}
React.useEffect(() => {
convertTime(clock.timeLeft)
if (clock.timeLeft === 0) {
document.querySelector('#beep').play()
setTimeout(() => {
updateLabel()
}, 1000)
}
}, [clock.timeLeft, convertTime])
startRun is a function that set the reference to the timeout callback, so that we can clearTimeout after, when necessary in our code. This function runs the action updateTimeLeft after 1 second. updateTimeLeft just send an action type to the reducer that decrement the timeLeft in our state.
const startRun = () => {
setTimeoutRef(
setTimeout(() => {
updateTimeLeft()
}, 1000)
)
}
case UPDATE_TIME_LEFT:
return {
...state,
timeLeft: state.timeLeft !== 0 ? state.timeLeft - 1 : state.timeLeft,
}
If the timeLeft is 0, we do nothing and the update to the clock will be handled by another action type UPDATE_LABEL, checking if it should update using break length or session length.
Following the code, we have an effect, this effect is concerned about the clock running state, that tracks the running and timeLeft state from clock, it checks whether the clock is running or not, if it's, continue running, and the reference will be updated in the state. Studying and reading documentations I've realized that the appropriate here to store the reference of setTimeout callback would be use the useRef() react hook, since updates in the state with useState makes a re-render in the component, it works because effects live longer, its closure is created when the function was created so it can access its environment of variables, but again, today I think that useRef would be a better approach.
React.useEffect(() => {
if (clock.running) startRun()
else clearTimeout(timeoutRef)
}, [clock.running, clock.timeLeft])
handleRun just handle when the user clicks in the "pause or play" button and invoke the toggleRunning action, its reducer updates the state of clock.running.
The last effect tracks the time left in the clock state, convertTime is action that will convert seconds to minutes, a readbable time left, it checks if the time has reached 0 and notice that we have to wait 1 second before to trigger the updateLabel action, to update timeLeft, so it uses the length configured in the break length. This 1 second is important, otherwise the test will not pass, it shouldn't instantly update the state of time, but continues in the same "rhythm", second after second, for example, if the state it's 3 seconds remaining and the break length is 5 minutes, after updateLabel is invoked should have passed 4 seconds (the time from 0 to 5 minutes).
React.useEffect(() => {
convertTime(clock.timeLeft)
if (clock.timeLeft === 0) {
document.querySelector('#beep').play()
setTimeout(() => {
updateLabel()
}, 1000)
}
}, [clock.timeLeft, convertTime])
This was an incredible project to understand more about asynchronous programming, update and read state that can be updated after some time.
This project is using sass preprocessor to create the css file, sass allow us to build styles in a more flexible way like use of mixins, nested selectors '&' selector and so on.
This course teaches you how to use HTML, Javascript, CSS, Sass, Bootstrap, React, Redux and Jquery to build Web applications.