setTimeout, setInterval

Here are notes on setTimeout, setInterval, and related methods in JavaScript:

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1. setTimeout()

Definition:

setTimeout() is a function that executes a piece of code after a specified delay.

Syntax:

let timeoutID = setTimeout(callback, delay, param1, param2, ...);

• callback: Function to execute after the delay.

• delay: Time in milliseconds (1000 ms = 1 second).

• param1, param2, ...: Optional parameters to pass to the callback function.

• timeoutID: Returns a unique ID for clearing the timeout.

Example:

setTimeout(() => {
    console.log("Executed after 2 seconds");
}, 2000);

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2. clearTimeout()

Definition:

clearTimeout() is used to cancel a timeout set by setTimeout().

Syntax:

clearTimeout(timeoutID);

• timeoutID: The ID returned by setTimeout().

Example:

let timer = setTimeout(() => {
    console.log("This will not execute");
}, 3000);

clearTimeout(timer); // Cancels the timeout before execution

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3. setInterval()

Definition:

setInterval() repeatedly executes a function after a specified interval.

Syntax:

let intervalID = setInterval(callback, delay, param1, param2, ...);

• callback: Function to execute at each interval.

• delay: Time in milliseconds between executions.

• intervalID: Returns a unique ID for clearing the interval.

Example:

let count = 0;
let interval = setInterval(() => {
    count++;
    console.log("Repeating every 1 second:", count);
}, 1000);

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4. clearInterval()

Definition:

clearInterval() is used to stop an interval set by setInterval().

Syntax:

clearInterval(intervalID);

• intervalID: The ID returned by setInterval().

Example:

let counter = 0;
let interval = setInterval(() => {
    counter++;
    console.log("Counting:", counter);
    if (counter === 5) {
        clearInterval(interval); // Stops after 5 counts
        console.log("Interval Stopped!");
    }
}, 1000);

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5. setImmediate() (Node.js only)

• Executes a function as soon as the current event loop cycle finishes.

• Works similarly to setTimeout(fn, 0), but setImmediate() executes before timers.

Example:

setImmediate(() => {
    console.log("Executed immediately after I/O tasks");
});

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6. process.nextTick() (Node.js only)

• Executes a function before any I/O tasks or timers.

• Higher priority than setImmediate().

Example:

process.nextTick(() => {
    console.log("Executed before setImmediate");
});

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Differences Between setTimeout() and setInterval()

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Best Practices:

1. Always store the ID returned by setTimeout() or setInterval() for later clearing.

2. Use clearTimeout() and clearInterval() to prevent memory leaks.

3. Avoid using setTimeout() inside a loop; instead, use recursion if needed.

4. Prefer setImmediate() and process.nextTick() in Node.js for event-driven tasks.