Why on earth does null == "0" give false as a result?

amitshrivastavafcc · February 9, 2018, 3:07pm

So, i am now totally confused , javascript says one thing and then does totally opposite , i went to articles and videos to read about == and === , they all said == makes values convert to number …

So how on earth when Number(null) = 0 and Number(false) is 0 , do i get null == “0” as false , please guide me here …

Thanks

anon52159105 · February 9, 2018, 3:11pm

The type of null is weirdly considered an object, whileas the type of “0” is a string. == compares the values, === also compares the types. null is not equal to zero, however the Number() function when given no value (null is considered no value) will return “0”, if given a non-numerical value it will return “NaN” (not a number error). Because of this null is not equal to “0”.

amitshrivastavafcc · February 9, 2018, 3:15pm

@anon52159105 - thanks, i did not get the last part

if given a non-numerical value it will return “NaN” (not a number error). Because of this null is not equal to “0”.

In console when i type Number(null) , its giving 0 , can you please guide a bit more …

Thanks

anon52159105 · February 9, 2018, 3:51pm

null is the same as providing no value to the function, e.g. it’s ignored, because of this the Number() function returns a default value of zero, providing a non-number value though will return “NaN”.

zhouxiang19910319 · February 9, 2018, 4:02pm

Here is a table you can always check if you are unsure

Also, give chapter 4 a read you will find some sort of explanation there.

github.com

getify/You-Dont-Know-JS/blob/master/types & grammar/ch4.md

# You Don't Know JS: Types & Grammar
# Chapter 4: Coercion

Now that we much more fully understand JavaScript's types and values, we turn our attention to a very controversial topic: coercion.

As we mentioned in Chapter 1, the debates over whether coercion is a useful feature or a flaw in the design of the language (or somewhere in between!) have raged since day one. If you've read other popular books on JS, you know that the overwhelmingly prevalent *message* out there is that coercion is magical, evil, confusing, and just downright a bad idea.

In the same overall spirit of this book series, rather than running away from coercion because everyone else does, or because you get bitten by some quirk, I think you should run toward that which you don't understand and seek to *get it* more fully.

Our goal is to fully explore the pros and cons (yes, there *are* pros!) of coercion, so that you can make an informed decision on its appropriateness in your program.

## Converting Values

Converting a value from one type to another is often called "type casting," when done explicitly, and "coercion" when done implicitly (forced by the rules of how a value is used).

**Note:** It may not be obvious, but JavaScript coercions always result in one of the scalar primitive (see Chapter 2) values, like `string`, `number`, or `boolean`. There is no coercion that results in a complex value like `object` or `function`. Chapter 3 covers "boxing," which wraps scalar primitive values in their `object` counterparts, but this is not really coercion in an accurate sense.

Another way these terms are often distinguished is as follows: "type casting" (or "type conversion") occur in statically typed languages at compile time, while "type coercion" is a runtime conversion for dynamically typed languages.

However, in JavaScript, most people refer to all these types of conversions as *coercion*, so the way I prefer to distinguish is to say "implicit coercion" vs. "explicit coercion."

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amitshrivastavafcc · February 9, 2018, 5:17pm

@zhouxiang19910319 “42” is indeed truthy, but “42” == true is not performing a boolean test/coercion at all, no matter what your brain says. “42” is not being coerced to a boolean (true), but instead true is being coerced to a 1, and then “42” is being coerced to 42.`
Ok so this is what i read, it clearly says what i mentioned that == performs check by converting to number …

So is it the case that in case of null, it does not take it as Number(null) , then what does it take the value to be , i could not find any explanation for this edge case , can you please guide a bit more , like what is the value of null coerced to in this case … thanks for your time…

amitshrivastavafcc · February 9, 2018, 5:31pm

@anon52159105 - i am really sorry i am still a bit confused even after reading after stuff, what does null get coerced to in this case of using == , like null == “0” , does it is attempted to be ToString, ToNumber ?

Thanks

anon52159105 · February 9, 2018, 5:38pm

Null is not equal to 0 because null is a value, it as far as the language is concerned is nothingness.

PortableStick · February 9, 2018, 6:03pm

null does not get coerced into a number. Per the JavaScript specification, null is only loosely equal to null and undefined. It doesn’t get ToNumber, ToString, or any other internal function called on it. Good observation and great question, though.

John-freeCodeCamp · February 9, 2018, 6:31pm

0 is a number, null is nothing.

You can’t put the definition of null as itself, so they put 0 to represent no value.

Prove me wrong, but by logic that’s what I would think.

zhouxiang19910319 · February 10, 2018, 1:11am

I see thanks! (20 character)

Soupedenuit · February 10, 2018, 1:13am

I edited the title to make it grammaticaly correct.

RadDog25 · February 10, 2018, 5:49am

If "0" could be coerced to equal null then I’d expect it to also coerce to false, which would be strange because if("0") {} would be ignored.

Actually, PHP will treat "0" as a falsy value, and I feel Javascript got things right in this case.

robicombi · February 14, 2018, 12:21am

Zero is a numeric value, null is a reference to nothing.