How Can I Ensure a Function Called with `setInterval` Executes Only Once?

Managing Scheduled Functions with setInterval and clearInterval

Consider the following code fragment:

function doKeyDown(event) {
    switch (event.keyCode) {
        case 32:
            /* Space bar was pressed */
            if (x == 4) {
                setInterval(drawAll, 20);
            }
            else {
                setInterval(drawAll, 20);
                x += dx;
            }
            break;
    }
}

The goal is to call the drawAll function only once, not create a loop that repeatedly invokes it.

Using clearInterval to Stop Recurring Execution

setInterval establishes a recurring timer that calls the specified function periodically. To cease its execution, we can utilize clearInterval. Here's how it works:

var handle = setInterval(drawAll, 20);

// When you want to stop it:
clearInterval(handle);
handle = 0; // Indication of an uncleared interval

On browsers, the handle is guaranteed to be a non-zero numerical value. Thus, setting handle = 0 serves as a convenient flag to indicate that the interval has been cleared.

Scheduling a One-time Function Call

If the intention is to execute a function only once, consider using setTimeout instead. This function schedules a function to be invoked after a specified time interval but doesn't continue firing it thereafter. It also returns a handle for potential cancellation.

setTimeout(drawAll, 20);

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