无法获取以JavaScript结尾的月份中的31天

Question

I am putting an easter egg into my program that causes a jack-o-lantern image to appear on Halloween, but I cannot get the code to recognize October 31st as a month/day. When I do a console.log on my code, it feeds back "Mon Oct 30 2017" instead of the 31st.

var today = new Date();
var halloween = new Date(today.getFullYear() + '10-31');
console.log(halloween.toDateString());
console.log(today.toDateString());

if (today.toDateString() === halloween.toDateString()) {
    printedMsg.innerHTML = rewardMsg + 'You deserve a spooky treat! ' + 
    '<img src="https://preview.c9users.io/mkrul/color_project/reward-imgs/boo.jpg">';
}

EDIT: I put the missing hyphen in front of '-10-31', but the console is still showing me "Mon Oct 30 2017"

var halloween = new Date(today.getFullYear() + '-10-31');

Answer 1

You are missing a hyphen:

var today = new Date();
var halloween = new Date(today.getFullYear() + '-10-31');
console.log(halloween.toDateString());

Will return

Tue Oct 31 2017

Answer 2

In ECMAScript, parsing strings is problematic, and even if you get the format right, you're passing a date format that will be treated as UTC so represent the day before the day you want for users west of Greenwich.

Also see Why does Date.parse give incorrect results?

So don't rely on the built-in parser, pass the components directly:

 var halloween = new Date(new Date().getFullYear(), 9, 31); console.log('Halloween is on ' + halloween.toString());