Execute the setInterval function without delay the first time

Solution 1:

It's simplest to just call the function yourself directly the first time:

foo();
setInterval(foo, delay);

However there are good reasons to avoid setInterval - in particular in some circumstances a whole load of setInterval events can arrive immediately after each other without any delay. Another reason is that if you want to stop the loop you have to explicitly call clearInterval which means you have to remember the handle returned from the original setInterval call.

So an alternative method is to have foo trigger itself for subsequent calls using setTimeout instead:

function foo() {
   // do stuff
   // ...

   // and schedule a repeat
   setTimeout(foo, delay);
}

// start the cycle
foo();

This guarantees that there is at least an interval of delay between calls. It also makes it easier to cancel the loop if required - you just don't call setTimeout when your loop termination condition is reached.

Better yet, you can wrap that all up in an immediately invoked function expression which creates the function, which then calls itself again as above, and automatically starts the loop:

(function foo() {
    ...
    setTimeout(foo, delay);
})();

which defines the function and starts the cycle all in one go.

Solution 2:

I'm not sure if I'm understanding you correctly, but you could easily do something like this:

setInterval(function hello() {
  console.log('world');
  return hello;
}(), 5000);

There's obviously any number of ways of doing this, but that's the most concise way I can think of.

Solution 3:

I stumbled upon this question due to the same problem but none of the answers helps if you need to behave exactly like setInterval() but with the only difference that the function is called immediately at the beginning.

Here is my solution to this problem:

function setIntervalImmediately(func, interval) {
  func();
  return setInterval(func, interval);
}

The advantage of this solution:

• existing code using setInterval can easily be adapted by substitution
• works in strict mode
• it works with existing named functions and closures
• you can still use the return value and pass it to clearInterval() later

Example:

// create 1 second interval with immediate execution
var myInterval = setIntervalImmediately( _ => {
        console.log('hello');
    }, 1000);

// clear interval after 4.5 seconds
setTimeout( _ => {
        clearInterval(myInterval);
    }, 4500);

To be cheeky, if you really need to use setInterval then you could also replace the original setInterval. Hence, no change of code required when adding this before your existing code:

var setIntervalOrig = setInterval;

setInterval = function(func, interval) {
    func();
    return setIntervalOrig(func, interval);
}

Still, all advantages as listed above apply here but no substitution is necessary.