Calculate Time Difference with JavaScript

Question

I have two HTML input boxes, that need to calculate the time difference in JavaScript onBlur (since I need it in real time) and insert the result to new input box.

F

Answer 1

tl;dr

One off run

const t1 = new Date(1579876543210) // your initial time
const t2 = new Date(1579987654321) // your later time

const diff = t2-t1
const SEC = 1000, MIN = 60 * SEC, HRS = 60 * MIN
const humanDiff = `${Math.floor(diff/HRS)}:${Math.floor((diff%HRS)/MIN).toLocaleString('en-US', {minimumIntegerDigits: 2})}:${Math.floor((diff%MIN)/SEC).toLocaleString('en-US', {minimumIntegerDigits: 2})}.${Math.floor(diff % SEC).toLocaleString('en-US', {minimumIntegerDigits: 4, useGrouping: false})}`

console.log("humanDiff:", humanDiff)
// > humanDiff: 30:51:51.0111

As a function

function humanDiff (t1, t2) {
  const diff = Math.max(t1,t2) - Math.min(t1,t2) 
  const SEC = 1000, MIN = 60 * SEC, HRS = 60 * MIN
  
  const hrs = Math.floor(diff/HRS)
  const min = Math.floor((diff%HRS)/MIN).toLocaleString('en-US', {minimumIntegerDigits: 2})
  const sec = Math.floor((diff%MIN)/SEC).toLocaleString('en-US', {minimumIntegerDigits: 2})
  const ms = Math.floor(diff % SEC).toLocaleString('en-US', {minimumIntegerDigits: 4, useGrouping: false})
  
  return `${hrs}:${min}:${sec}.${ms}`
}

const t1 = new Date(1579876543210)
const t2 = new Date(1579987654321)

console.log("humanDiff(t1, t2):", humanDiff(t1, t2))
// > humanDiff: 30:51:51.0111

Explanation

Adjust humanDiff for your maximum and minimum reportable increments and formatting needs:

const t1 = new Date(1579876543210) // Set your initial time (`t1`)
const t2 = new Date(1579986654321) // , conclusion time (`t2`), and
const diff = t2-t1 // calculate their difference in milliseconds
console.log("         t2:", t2.toISOString()) // >   t2: 2020-01-25T21:27:34.321Z
console.log("         t1:", t1.toISOString()) // >   t1: 2020-01-24T14:35:43.210Z
console.log("       diff:", diff)             // > diff: 111111111

// Set your constant time values for easy readability
const SEC = 1000
const MIN = 60 * SEC
const HRS = 60 * MIN

/* For a given unit
1) disregard any previously relevant units, e.g. to calculate minutes, we can
   disregard all hours & focus on only the remainder - `(diff%HRS)`
2) divide the remainder by the given unit, e.g. for minutes, `(diff%HRS)/MIN`
3) disregard any remainder, e.g. again for minutes, `Math.floor((diff%HRS)/MIN)`
NOTE: for your maximum unit (HRS in the examples below) you probably _don't_
  want to disregard high values, e.g. If the difference is >24 hrs and something,
  you should either include a DAYS value, or simply display 30 hrs */
let hrs = Math.floor(diff/HRS)
let min = Math.floor((diff%HRS)/MIN)
let sec = Math.floor((diff%MIN)/SEC)
let ms  = Math.floor(diff % SEC) // just the remainder 
          // BUT ms IS NOT ACTUALLY CORRECT, see humanDiff_3 for the fix ;-)
let humanDiff_1 = `${hrs}:${min}:${sec}.${ms}`
console.log("humanDiff_1:", humanDiff_1)
// > humanDiff_1: 30:51:51.111

sec = Math.round((diff%MIN)/SEC) // can also just round the last unit
const humanDiff_2 = `${hrs} hrs ${min} mins & ${sec} secs`
console.log("humanDiff_2:", humanDiff_2)
// > humanDiff_2: 30 hrs 51 mins & 51 secs

/* To ensure a set number of digits, format the numbers with `toLocaleString`'s
   `minimumIntegerDigits`, if more than 3 digits, also use its `useGrouping`   */
hrs = Math.floor(diff/HRS)
min = Math.floor((diff%HRS)/MIN).toLocaleString('en-US', {minimumIntegerDigits: 2})
sec = Math.floor((diff%MIN)/SEC).toLocaleString('en-US', {minimumIntegerDigits: 2})
ms = Math.floor(diff % SEC).toLocaleString('en-US', {minimumIntegerDigits: 4, useGrouping: false})

const humanDiff_3 = `${hrs}:${min}:${sec}.${ms}`
console.log("humanDiff_3:", humanDiff_3)
// > humanDiff_3: 30:51:51.0111
// NOTE: milliseconds are now 4 digits