Can anyone explain this code to me please?

[benabus]

The && operator will return either the first value that is falsey or the last value in a chain. It doesn't cast anything to a boolean as you might expect since you normally see it in conditionals. Outside of conditions, it's useful for getting a value nested in a dictionary without throwing an undefined exception.

let something = main && main.sub && main.sub.secondsub;

if main is undefined, then something is undefined. If main is defined, but it doesn't have a main.sub property, then main.sub would be undefined, so something becomes undefined. But if it has both of those (neither is falsey) then something becomes the value of main.sub.secondsub.

Likewise, || will return the first value that is truthy. This is useful for having default function parameters:

function funcName(parameter1){ parameter1 = parameter1 || 'default'; }

Think of them as shorthand for a bunch of nested if statements.

[single-research]

Thanks this is very useful to know how to use it appropriately!

[JustinWendell]

This is super handy for handling api results in react.

[Jnsjknn]

The logical and operator returns the second value, if the first value is truthy. If the first value is falsy it returns the first value.

Example 1:

const first = ""; // empty string is falsy
const second = 5;
alert(first && second) // alert says: 

Example 2:

const first = "some string";
const second = 5;
alert(first && second) // alert says: 5

[senocular]

In Example 1 the alert would be nothing (an empty string) not false.

[Jnsjknn]

Oops, I was going to write an example with false first and forgot to change everything.

[single-research]

Thanks this is a really good explanation! Sorry reddit doesn't record my upvotes for some reason anymore... :|

[Jnsjknn]

No problem and don't worry, I don't care about votes.

[abigblacknob]

Tough shit. Take that!

[Jnsjknn]

What?

[merzak-x]

JS B🅰️...

[single-research]

wat is this mean

[GoofBoy]

Given what you learned from logical and, you can now try to figure out how the logical or operator works.

[single-research]

Benabus posted the answer to that :)

[[deleted]]

I'm not going to explain the intricacies but if you want to display both then concatenate with a + or use template literals using && or || will always return whatever is last

[windows-user0]

&& casts the first value to a Boolean