uncaught type error… is not a function

Question

I am practicing this simple countdown function in the console and the code works once I completed writing it and hit enter, but when I try to call it again (typed countDown(); ), the console gives me this error message saying

"Uncaught TypeError: countDown is not a function".

I save the function in the variable countDown and when I called the function, I simply typed countDown(); I checked there is no typing error. What did I do wrong, the code is as below...

var timeLeft = 10;
var countDown = setInterval(function(){
  timeLeft--;
  console.log(timeLeft);
  if(timeLeft === 0){
    clearInterval(countDown)
    console.log("count down completed")
  }
} ,1000);

Answer 1

I save the function in the variable countDown

No, you saved _the result of setInterval in that variable.

setInterval returns a timer ID, not a function.

If you want to save a function in a variable, you need to actually save the function in the variable.

Answer 2

I think you should declare the function outside setInterval, I've provided below example for your reference:

var timeLeft  = 10;
var countDown  = setInterval(timer, 1000 );

function timer() {
   console.log(timeLeft);
   if (timeLeft < 1) {
      console.log('Count down completed'); 
      clearInterval(countDown);
      return;         
   } 
   timeLeft  -= 1;
}