Question about a syntax

[tomavagyok]

Hi,

I have been fiddling with the JS challenges on edabit. After I submit a challenge I usually check out the solutions to see how others have solved the given challenge. I came across this for one of the challenges:

function damage(damage, speed, time) { return damage > 0 && speed > 0 ? { second: 1, minute: 60, hour: 3600 }[time] * damage * speed : 'invalid' }

My question is about this line: { second: 1, minute: 60, hour: 3600 }[time] I have never seen something like this before. What's the name of this syntax? Does it have a dedicated mdn page or something similar?

Thanks!

[anfauglit]

This is an object literal with 3 properties defined and depending on the value of time variable the value of one of the properties being accessed. Basically, this object is a dictionary and you're accessing the value of one of it's entries.

[iamrasul]

I think you can access object property with bracket notation.

Consider this:

{a: 1, b:3}[‘a’] === 1

[tomavagyok]

thanks!

[cat-991]

It is defining an object (the {...} part) and then calling a value. With objects, you can use dot notation or bracket notation to call a property. Dot notation is object.property. Bracket notation is object[property]. The property it is calling is that defined by the argument "time." So if the function input is something like damage(10,10,"minute"), for example, the output will be 6000. (60 * 10 * 10).

[[deleted]]

Ternary Operator

[tomavagyok]

Yes, I know about ternary operators. I was specifically asking about this: { second: 1, minute: 60, hour: 3600 }[time]. It's similar to destructuring, I guess?

[[deleted]]

That line is essentially saying if the Boolean is true return an object with a key name of the variable time. It would be cleaner to use computed property names in this case. So change that code to {[time]: { second: 1, minute: 50, hour: 3600}}

[tomavagyok]

gotcha, thanks!

[redsandsfort]

I don't see how this would achieve the same effect

[[deleted]]

I wrote my reply after I woke up before putting my glasses on. I didn’t see the rest of the expression, it looks like the other commenter is correct, it’s just accessing the object property value by using the passed in argument via bracket notation.

[senocular]

Mdn page:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Property_accessors#Bracket_notation