typeof !== "undefined", comparing dates, new Date, Math.min / What is wrong with this simple js code?

Question

This code is on my nodeJS server. Every time the server gets to it, it crashes. Don't know what's wrong... Could someone help me?

dateArray[11], dateArray[12] and dateArray[13] are either empty or are Date values.

var dateArray11 = null;
var tempDateValue = "";
if ((typeof dateArray[11] !== "undefined") || (typeof dateArray[12] !== "undefined") || (typeof dateArray[13] !== "undefined")) {
    dateArray11 = new Date(Math.min((dateArray[11].getTime()), (dateArray[12].getTime()), (dateArray[13].getTime())));
    if (dateArray11.getTime() === dateArray[11].getTime()) {
        tempDateValue = 11;
    }
    if (dateArray11.getTime() === dateArray[12].getTime()) {
        tempDateValue = 12;
    }
    if (dateArray11.getTime() === dateArray[13].getTime()) {
        tempDateValue = 13;
    }
}

You could make sure they're date objects by using `instanceof Date`. — Ben Fortune, Sep 09 '16 at 15:44
That's what I was trying to do with (typeof Date !== "undefined"). Is it wrong? Didn't have any issues with it till now... — Emilio, Sep 09 '16 at 15:47
not really, I want it to be "if at least one of them exists, take the lowest date of the ones that exist, then define the corresponding tempDateValue" But maybe I can't use .getTime() with values that don't exist. Maybe it is the issue!? — Emilio, Sep 09 '16 at 15:58
Saying the server "crashes" means something different from the server "issues a run-time error". — , Sep 09 '16 at 19:09
@torazaburo Thanks for letting me know! I will use the appropriate terminology next time! — Emilio, Sep 09 '16 at 19:42

abdulbarik · Answer 1 · 2016-09-09T16:19:26.273

0

typeof(new Date()) is always give you an object and you are comparing it with String since typeof("undefined") is String.

console.log(typeof 123)// return number

console.log(typeof new Date())// return object

console.log(typeof 'hola')//return string

The typeof operator returns type information as a string. There are six possible values that typeof returns: "number," "string," "boolean," "object," "function," and "undefined." The parentheses are optional in the typeof syntax.

edited Sep 09 '16 at 16:19

answered Sep 09 '16 at 15:54

abdulbarik

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typeof is an operator that always returns a string, describing the type of a value ... see for example: http://stackoverflow.com/a/5663356/6814172 – Emilio Sep 09 '16 at 16:01
Nope it'll not return always `String` console.log(typeof(new Date())); it'll return `object` – abdulbarik Sep 09 '16 at 16:02
Do you have some reference? This page says it always returns a string: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/typeof . – Emilio Sep 09 '16 at 16:07
Can you print above console in your browser's console? – abdulbarik Sep 09 '16 at 16:08
see the reference here https://msdn.microsoft.com/en-us/library/259s7zc1(v=vs.94).aspx – abdulbarik Sep 09 '16 at 16:10
search `typeof operator in javascript` Google give you exact answer – abdulbarik Sep 09 '16 at 16:11
If still you have doubt then you can print above console and clear your doubt – abdulbarik Sep 09 '16 at 16:13
My console won't be much help because it only says "POST /submitDetails 500 35.562 ms - 1314". – Emilio Sep 09 '16 at 16:17
By the way, the link you gave me says typeof always returns a string. – Emilio Sep 09 '16 at 16:18

score 0 · Accepted Answer · edited May 23 '17 at 12:08

0

Since you said that dateArray[11], dateArray[12] and dateArray[13] are either empty or are Date values.

You cannot call a getTime() function of an empty or undefined value.

Before you call it, you should check if dateArray[11], dateArray[12] and dateArray[13] are Date Objects. You can see how to check that in this answer: https://stackoverflow.com/a/643827/3442014

EDIT: This is my aproach of what you're doing:

var dateArray=[];
dateArray[11]=new Date("2011/06/31");
dateArray[12]=new Date("2011/06/26");
dateArray[13]="";

var tempDateValue = "";

var dates=[];
if (dateArray[11] instanceof Date) dates.push(dateArray[11]);
if (dateArray[12] instanceof Date) dates.push(dateArray[12]);
if (dateArray[13] instanceof Date) dates.push(dateArray[13]);

var min = new Date(Math.min.apply(null,dates));

var tempDateValue = dates.map(Number).indexOf(+min) + 11;

edited May 23 '17 at 12:08

Community

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answered Sep 09 '16 at 16:10

Federicorp

76
5

it'll not give object type of Date it just give you object even if you check typeof null, it will give you `object` :) – abdulbarik Sep 09 '16 at 16:18
@Federicorp As I said, I want it to be : "if at least one of them exists, take the lowest date of the ones that exist, then define the corresponding tempDateValue" . So you're right, this is the issue, but I don't want to check if dateArray[11], dateArray[12] AND dateArray[13] are Date Objects, because not all of them are. I will have to find another way to make it work. – Emilio Sep 09 '16 at 16:20
Thanks for your elaborate answer! In the meantime I figured it out. The part I was missing was that I didn't need to .getTime() date values in an array before I could Math.min.apply(null, the array. – Emilio Sep 09 '16 at 19:57

typeof !== "undefined", comparing dates, new Date, Math.min / What is wrong with this simple js code?

2 Answers2