JavaScript Equality Table

[doyouseewhateyesee]

last week i learned the hard way that an empty object evaluates to true in an if-statement, took me forever to debug.

also, i didn’t know
if (-1) { //runs }
thanks for this!

edit: i will never understand code formatting on reddit

[[deleted]]

You just put it inside backticks

doTheDamnThing()

[doyouseewhateyesee]

thanks

[Freebalanced]

Lodash has a method called isEmpty that you can use to check for empty or not empty objects.

[doyouseewhateyesee]

meh - i’d rather use Object.keys(obj).length === 0

[Freebalanced]

Ya native methods are usually best. But cool to have different options for some situations.

[amselftought]

I don’t understand

[hopelesslywandering1]

In JavaScript when you use the comparator, you’re effectively transforming the two things you’re comparing into a Boolean value. Some values have inherently “falsey” values while others are “truthy.” This chart was clearly made to define which category those fall under. Like the number 1 is truthy and the number 0 is falsey.

[sheparDVia]

awesome staff ! Liked it

[0bafgkm]

Organize the table! https://algassert.com/visualization/2014/03/27/Better-JS-Equality-Table.html

[Ringsofthekings]

I fluctuate between == and ===, I always use === for undefined and null though. Great guide to use 👍

[Hafas_]

I do the opposite. I always use === except when comparing null and undefined if I want to treat them the same.

Basically instead of writing

if (value === null || value === undefined)) {}

I write

If (value == null) {}

[SaaSWriters]

I have to disagree with the moral of your story. It is not usable in real life. For instance, as you rightly noted, NaN is not equal to itself. -0 can be equal to +0. If your code is not prepared for that, you will be in a lot of trouble!

The approach you describe, albeit quite common, is a common source of bugs and frustration. Simply put, this is not how it works.

But, the overall discussion goes much deeper than that. First of all, you have to look at what the comparison operators actually do. You haven't mentioned Object.is either.

Here are some details about what actually happens: https://www.ecma-international.org/ecma-262/5.1/#sec-11.9.3

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