Scheduling: setTimeout and setInterval

Scheduling in JavaScript: setTimeout & setInterval

JavaScript provides two main scheduling functions to execute code after a delay or repeatedly at intervals:

1. setTimeout → Runs a function once after a delay.
2. setInterval → Runs a function repeatedly at fixed intervals.

1️⃣ setTimeout – Delayed Execution

setTimeout executes a function after a specified time (in milliseconds).

Syntax

setTimeout(function, delay, param1, param2, ...);

• function → Function to execute
• delay → Time in milliseconds (1 second = 1000 ms)
• param1, param2, ... → Optional parameters for the function

Example: Delay Execution by 2 Seconds

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

Example: Passing Arguments

function greet(name) {
    console.log(`Hello, ${name}!`);
}

setTimeout(greet, 3000, "Alice"); // Runs after 3 seconds

Cancel setTimeout with clearTimeout

If you need to cancel a scheduled timeout, use clearTimeout.

const timeoutId = setTimeout(() => {
    console.log("This will not run.");
}, 5000);

clearTimeout(timeoutId); // Cancels the timeout

2️⃣ setInterval – Repeated Execution

setInterval executes a function at regular intervals (repeats indefinitely).

Syntax

setInterval(function, interval, param1, param2, ...);

• function → Function to execute
• interval → Time interval in milliseconds
• param1, param2, ... → Optional parameters

Example: Run Every 1 Second

setInterval(() => {
    console.log("This runs every second.");
}, 1000);

Example: Passing Arguments

function showTime(name) {
    console.log(`${name}, current time is: `, new Date().toLocaleTimeString());
}

setInterval(showTime, 2000, "Alice"); // Runs every 2 seconds

Cancel setInterval with clearInterval

To stop a repeating interval, use clearInterval.

const intervalId = setInterval(() => {
    console.log("This will repeat every 2 seconds.");
}, 2000);

setTimeout(() => {
    clearInterval(intervalId); // Stops the interval after 6 seconds
    console.log("Interval stopped.");
}, 6000);

3️⃣ When to Use setTimeout vs. setInterval?

Feature	setTimeout	setInterval
Runs once?	✅ Yes	❌ No (Repeats)
Runs repeatedly?	❌ No	✅ Yes
Can be canceled?	✅ clearTimeout()	✅ clearInterval()
Best for?	Delayed execution	Periodic updates

4️⃣ Alternative to setInterval – Recursive setTimeout

A better alternative to setInterval is using recursive setTimeout, which ensures accurate timing.

function repeatTask() {
    console.log("Task executed!");
    setTimeout(repeatTask, 2000); // Calls itself after 2 seconds
}

repeatTask();

✅ Why use this?

• Prevents overlapping executions if a previous task is still running.
• More accurate than setInterval for long tasks.

Conclusion

✔ setTimeout → Executes a function once after a delay.
✔ setInterval → Repeats execution at fixed intervals.
✔ Use clearTimeout / clearInterval to cancel scheduled tasks.
✔ For more control, use recursive setTimeout instead of setInterval.

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