Timers

In Javascript, timers are used to execute code at specific times or execute code repeatedly after a certain amount of time. JavaScript provides two main types of timers: setTimeout() and setInterval(). Both allow you to schedule code to run after a specific delay, but they behave differently.

1. setTimeout()

• setTimeout() allows you to run a function or a block of code after a specified delay, but it only executes the code once.
• How it works:- You tell JavaScript, "Wait for this amount of time, and then run this code."

Syntax

setTimeout(function, delay, ...args);

Example

function sayHello() {
  console.log("Hello, world!");
}

// Call sayHello() after 3 seconds (3000 milliseconds)
setTimeout(sayHello, 3000);

In this example, the sayHello function will run after 3 seconds. The setTimeout() function takes two arguments:

• The function you want to run (sayHello).
• The delay in milliseconds (3000 milliseconds = 3 seconds).
• ...args (optional): Additional arguments that will be passed to the function when it executes.

Important Points:

• Non-blocking: setTimeout() does not block the rest of the code from executing. JavaScript continues to execute other instructions while it waits for the timeout.
• Milliseconds: The delay is specified in milliseconds, and the minimum delay is 1 millisecond.
• Single Execution: After the specified time, the callback function is invoked only once.

2. setInterval()

• setInterval() repeatedly runs a piece of code or function at a specified interval (in milliseconds), until you tell it to stop.
• How it works:- You tell JavaScript, "Keep running this code every X amount of time."

Syntax

setInterval(function, interval, ...args);

Example

function sayHello() {
  console.log("Hello again!");
}

// Call sayHello() every 2 seconds (2000 milliseconds)
setInterval(sayHello, 2000);

• Here, the code inside setInterval() will run every 2 seconds.

Important Points:

• Non-blocking: Similar to setTimeout(), setInterval() is non-blocking. The browser continues running other tasks while it waits for the next interval.
• Repeats: Unlike setTimeout(), which runs only once, setInterval() will keep executing the callback function at the specified interval.
• Continuing Until Stopped: The function will run continuously at the given interval until it is cleared manually.

Clearing Timers

Sometimes, you might want to stop a timer before it completes. You can do this with clearTimeout() and clearInterval().

Stopping the setTimeout() timer:

If you want to cancel the timeout before it executes, you can use clearTimeout():

function sayHello() {
  console.log("Hello, world!");
}
const timeoutId = setTimeout(sayHello, 4000);

// Stop the timeout before it runs
clearTimeout(timeoutId);

Stopping the setInterval() timer:

const intervalId = setInterval(sayHello, 1000);

// Stop the interval after 5 seconds
setTimeout(() => {
  clearInterval(intervalId);
  console.log("Interval timer stopped");
}, 5000);

• Here, we first start an interval that runs every second. Then, after 5 seconds, we use setTimeout() to stop the interval using clearInterval(intervalId).

Summary of Key Concepts:

• setTimeout(): Executes a function once after a specified delay.
• setInterval(): Executes a function repeatedly at specified intervals.
• clearTimeout() / clearInterval(): Used to cancel timers.
• Asynchronous nature: Timers do not block the execution of other code; they are added to the event queue and executed once the call stack is empty.
• Accuracy: Timer accuracy is not guaranteed due to other factors like heavy computations or browser limitations.