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JavaScript: Count the number of days passed since beginning of the year

JavaScript Datetime: Exercise-16 with Solution

Write a JavaScript function to count the number of days passed since beginning of the year.

Test Data:
console.log(days_passed(new Date(2015, 0, 15)));
15
console.log(days_passed(new Date(2015, 11, 14)));
348

Sample Solution:-

HTML Code:

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JavaScript function to count the number of days passed since beginning of the year</title>
</head>
<body>

</body>
</html>

JavaScript Code:

function days_passed(dt) {
  var current = new Date(dt.getTime());
  var previous = new Date(dt.getFullYear(), 0, 1);

  return Math.ceil((current - previous + 1) / 86400000);
}
console.log(days_passed(new Date(2015, 0, 15)));
console.log(days_passed(new Date(2015, 11, 14)));

Sample Output:

15
348

Flowchart:

Flowchart: JavaScript- Count the number of days passed since beginning of the year

Live Demo:

See the Pen JavaScript - Count the number of days passed since beginning of the year-date-ex- 16 by w3resource (@w3resource) on CodePen.


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Next: Write a JavaScript function to convert a Unix timestamp to time.

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JavaScript: Tips of the Day

Promise.all method

const promise1 = Promise.resolve('First')
const promise2 = Promise.resolve('Second')
const promise3 = Promise.reject('Third')
const promise4 = Promise.resolve('Fourth')

const runPromises = async () => {
	const res1 = await Promise.all([promise1, promise2])
	const res2  = await Promise.all([promise3, promise4])
	return [res1, res2]
}

runPromises()
	.then(res => console.log(res))
	.catch(err => console.log(err))

The Promise.all method runs the passed promises in parallel. If one promise fails, the Promise.all method rejects with the value of the rejected promise. In this case, promise3 rejected with the value "Third". We're catching the rejected value in the chained catch method on the runPromises invocation to catch any errors within the runPromises function. Only "Third" gets logged, since promise3 rejected with this value.