4 not so crucial things I didn't know about JavaScript

There is so many things that you don't know about JavaScript. Some are crucial, some are not. I wanted to put some not so crucial observations that I didn't know about JavaScript to blog post. Hope you will find them interesting. Let's get to it.

Just plain scope

Thing number one in this list is that you can use just plain { ... } scope whenever you want.

let name = 'Big Lebowski';

{
    let nickname;
    if (name === 'Big Lebowski') {
        nickname = 'The Dude';
    } else {
        nickname = 'Walter';
    }
    // ...
}

console.log(nickname) // ReferenceError: nickname is not defined

This preserves the same functionality as other scopes withif, for, etc. But why would you use plain scope? Exactly why you are using lexical scoping in eg. function or if statements. To scope variables so they are not accessible from outer scope to prevent naming collision and keep things seperate. You can use these plain scopes to follow the principle of least privilege. Not once did I come across upon such usage in any codebase that I run into but that doesn't mean it's useless.

There is no else if in JS!

Wait, what?! I have used else if so many times and now it doesn't exist in JavaScript? The construction else if doesn't exists in the language AS IS. Only if / else exists. But how can I use else if then? Answer is easier that you might think. You just omit curly braces after else.

if (a === b) {
    // ...
} else if (a === c) {
    // ...
}

// is actualy following but with omitted curly braces after else

if (a === b) {

} else {
    if (a === c) {
        // ...
    }
}

Omitting curly braces is not anything special in JavaScript. Recall this:

const name = () => firstName + lastName;

Again, this is not anything crucial for your day to day life but just a fun fact.

Naming loops and other statements! WHAT?!

You can label JavaScript statement to afterwards use break or continue with the label.

loop1:
for (let i = 0; i < 3; i++) {      //The first for statement is labeled "loop1"
   loop2:
   for (let j = 0; j < 3; j++) {   //The second for statement is labeled "loop2"
      if (i === 1 && j === 1) {
         break loop1;
      }
   }
}

You can also use them with those plain scopes I mentioned at the beginning of this post.

someScope: {
    // ..
    break someScope
    // anything after break won't be executed
}

Again, I have not seen naming with label in any real codebase but that doesn't mean it doesn't have an use case for you in future.

There is negative zero!

Yes, there is -0 and it is valid. Since JavaScript uses IEEE 754 standard there are signed zeros (-0 and +0) and they are equal!

-0 == 0 // true
-0 === 0 // true

You can still tell the difference with following code

Object.is(-0, 0) // false
// or
1/0 === 1/-0; // false (1/0 === Infinity and 1/-0 === -Infinity)

Where negative zero occurs? In certain numeric operations such as

0 / -3; // -0
0 * -3; // -0

Another case is using negative zero with vector logic where besides value you also needs to know the direction of the value.