I am new to JavaScript and was learning about promises. I want to print 5 to 0 numbers at the interval of 2 seconds each. For example for the first time after 2 seconds print 5 and then after 2 second print 4 and so on. I have written a code to do so but not able to get the correct output.
var count = 5;
var i = 2;
function d()
{
let p = new Promise((resolve,reject)=>{
while(count>=0)
{
setTimeout(resolve,i*1000,count);
i= i*2;
count = count-1;
//count = count-1;
}
});
return p;
}
d().then((x)=>{
console.log(x);
});
It is showing output as 5. Can anyone correct it?
It's much easier to write this using the async ... await syntax... you can then create a pause function that will delay by timeout milliseconds.
We can wrap this in a while statement, looping until the count is zero.
async function pause(timeout) {
return new Promise(resolve => setTimeout(resolve, timeout))
}
async function countDown(count) {
while (count > 0) {
await pause(2000);
console.log('count:', count);
count--;
}
}
countDown(5);Whenever you are writing a program, it is a good idea to quantify what it is you need to keep track of.
In this case we have three components.
A basic for..loop let's us loop over the number range and queue up some setTimeout calls with our callback:
/**
* CountDown
*
* @param {Function} callback - The callback is a function that we call each "tick"
* @param {number} countDownFrom - The countdown starts at this number
* @param {number} interval - the number of milliseconds between each "tick"
*/
function CountDown(
callback,
countDownFrom,
interval
) {
for (var count = 0; count <= countDownFrom; count++) {
setTimeout(callback, (countDownFrom - count) * interval, count);
}
}
CountDown(
(x) => {
console.log(x);
},
5,
2 * 1000
);I have put some links to www.w3schools.com in this answer. There you can find documentation and tutorials for a lot of JavaScript problems.