Conditional statement inside a Math.min or a Math.max in JavaScript

Question

I want to Math.min a few Date values (e.g. var1.getTime(), var2.getTime(), and var3.getTime()). However, before I can use .getTime() on them, I need to make sure they exist (so the script doesn't crash).

If one of the variables doesn't exist I still want to get the Math.min of the other variables that exist.

Any clues?

Possible duplicate of [How might I find the largest number contained in a JavaScript array?](http://stackoverflow.com/questions/1379553/how-might-i-find-the-largest-number-contained-in-a-javascript-array) — Mike Cluck, Sep 09 '16 at 17:38
@Mike C Yes, but how do you make sure they exist before you put them in the Array? Because, if one of them don't exist .getTime() will make the script crash. And how do you .getTime() them before you Math.min them ? — Emilio, Sep 09 '16 at 17:50
@Emilio The same way that you check for anything. Only add them to the array of `someVar instanceof Date`. — Mike Cluck, Sep 09 '16 at 17:51
@Emilio: [Nothing at all?](https://www.youtube.com/watch?v=qf7rntVimhw) The code that gives you back the max/min Date or timestamp -- does it return nothing? `null`? Throw an exception? — Scott Sauyet, Sep 09 '16 at 17:58
Have you got a code snippet to share so we can give you useful advice? — jwpfox, Sep 09 '16 at 22:30

score 3 · Accepted Answer · edited Oct 09 '17 at 17:46

3

If you store your date variables in an array, you can use filter to remove non-Date objects and pass that to Math.min.apply or Math.max.apply

const dates = [var1, var2, var3];
const min = Math.min(...dates.filter(date => date instanceof Date));

Or non-ECMAScript 6:

var dates = [var1, var2, var3];
var min = Math.min.apply(null, dates.filter(function(date) {
  return date instanceof Date;
}));

edited Oct 09 '17 at 17:46

Peter Mortensen

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answered Sep 09 '16 at 17:40

Rob M.

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Yeah, but you still need to .getTime() them before you can Math.min them ? How do you do that? – Emilio Sep 09 '16 at 17:45
No you don't, dates are implicitly converted to numbers (their timestamp value) when mathematical operations are performed on them: `+new Date()` – Rob M. Sep 09 '16 at 17:46
@RobM. I see you updated the es6 code. Should we also update the non-es6 code or not? Thanks – Emilio Sep 09 '16 at 17:54
@Emilio, nope, es6 doesn't need `.apply` because of the spread operator, prior to es6 `.apply` was the way to achieve this – Rob M. Sep 09 '16 at 18:08
Great answer! I would just add a "new Date" to your answer in order to get back a date value. So, for non-es6, var dates = [var1, var2, var3]; var min = new Date(Math.min.apply(null, dates.filter(function(date) { return date instanceof Date; }))); – Emilio Sep 09 '16 at 19:50

Conditional statement inside a Math.min or a Math.max in JavaScript

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