Run function from setInterval once

Question

I have a setInterval function which is calculating the difference between a certain date and the current time. When this difference reaches less than an hour, I want to run some code that should only be executed once.

const countdownDate = new Date('March 15, 2021 11:30:00').getTime();
const HOUR_IN_MILLISECONDS = 3600000;

let ticker = setInterval(() => {
    let now = new Date().getTime();
    let duration = countdownDate - now;
    
    if (duration < HOUR_IN_MILLISECONDS) {
        console.log('This will keep running');
    }
    
    if (duration === 0) {
        clearInterval(ticker);
    }
}, 1000);

One method I've found to achieve this is by setting a global flag that is flipped once the function has run once.

let bar = false;

function foo() {
   if (!bar) {
       console.log('This will only run once');
   }
   bar = true;
}

let ticker = setInterval(() => {

    if (duration < HOUR_IN_MILLISECONDS) {
        foo();
    }

}, 1000);

Another way that works is to fire a custom event and register a one-off event handler. However i'm not sure if firing an event every second is less performant than the previous solution.

const foo = new Event('foo');

document.addEventListener('foo', () => {
    console.log('This will only run once');
}, { once: true });

let ticker = setInterval(() => {

    if (duration < HOUR_IN_MILLISECONDS) {
        document.dispatchEvent(foo);
    }

}, 1000);

I'm assuming there must be a better way to achieve the desired behaviour. I understand that it's not best practice to try run something only once inside a setInterval but i've not been able to find any other workarounds so far.

user_4399730 · Answer

you can use recursive function

  const start = (stop ,under)=>{
   let underHour = under;
   const countdownDate = new Date('March 15, 2021 11:30:00').getTime();
   const HOUR_IN_MILLISECONDS = 3600000;  
      if(!stop){
      setTimeout(function(){
                let now = new Date().getTime();
                let duration = countdownDate - now;
                if (!underHour) {
                  if (duration < HOUR_IN_MILLISECONDS) {
                    console.log('This will keep running');
                    underHour = true;
                  }
                }
    
                start(duration === 0, underHour);
            
       },1000)
    }
} 
 
//-----------
start()

Run function from setInterval once

1 Answers