Why Is My setInterval Function Only Running Once?

Understanding the setInterval Function and Its Execution

The setInterval function is a useful tool for scheduling tasks to run at regular intervals in JavaScript. However, developers may encounter issues where the callback function seems to execute only once instead of continuously.

The Issue: Callback Not Executing as Expected

One common reason for this behavior is an incorrect usage of the setInterval function call. The callback should be a function reference, not a function call.

Explanation: Function Call vs. Reference

In the case of the provided example:

window.setInterval(timer(), 1000)

There is a missing parenthesis after the timer function, causing it to be a function call rather than a reference. This results in the immediate execution of the timer function and subsequently sets the interval for the executed result, which is undefined.

Solution: Correcting the Syntax

To correct this issue and ensure continuous execution of the callback, use a function reference as follows:

window.setInterval(timer, 1000);

Alternatively, you can use an anonymous function as the callback, which is shorter but may reduce readability for larger functions:

window.setInterval( function() {
  console.log("timer!");
}, 1000)

This ensures that the timer function is scheduled to run at the specified interval of 1000 milliseconds.

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