JavaScript Timing Events

JavaScript Timing Events

With JavaScript, it is possible to execute some code after a specified time-interval. This is called timing events.

It's very easy to time events in JavaScript. The two key methods that are used are:

• setTimeout() - executes a code some time in the future
• clearTimeout() - cancels the setTimeout()

Note: The setTimeout() and clearTimeout() are both methods of the HTML DOM Window object.

The setTimeout() Method

Syntax

The setTimeout() method returns a value. In the syntax defined above, the value is stored in a variable called t. If you want to cancel the setTimeout() function, you can refer to it using the variable name.

The first parameter of setTimeout() can be a string of executable code, or a call to a function.

The second parameter indicates how many milliseconds from now you want to execute the first parameter.

Note: There are 1000 milliseconds in one second.

Example

When the button is clicked in the example below, an alert box will be displayed after 3 seconds.

Example - Infinite Loop

To get a timer to work in an infinite loop, we must write a function that calls itself.

In the example below, when a button is clicked, the input field will start to count (for ever), starting at 0.

Note: we also have a function that checks if the timer is already running, to avoid creating additional timers, if the button is pressed more than once:

The clearTimeout() Method

Syntax

Example

The example below is the same as the "Infinite Loop" example above. The only difference is that we have now added a "Stop Count!" button that stops the timer: