30-seconds-of-code: Value or default

[haojieguangxin]

Value or default

when value is 0, this function will return default value

[atomiks]

Also as it stands, it's quite useless because it takes longer with more overhead than just doing || d.

If we just don't want undefined, null, or NaN, but DO want to use the other falsy values:

const valueOrDefault = (value, d) => 
  (value || [false,0,''].includes(value)) ? value : d

[skatcat31]

I agree that valueOrDefault is kind of... weird. You have many other tools to accomplish it and should really only be checking for undefined(null in some of these cases is considered a specific value you'd want, same with NaN) so that only if something didn't return something when it should have would you need a default. If it returned null, and you wanted null you can't have it with this version.

[skatcat31]

also many prior arts call it defaultTo and make it a closure so you can use it in many similar cases:

const defaultTo = d => v => v === undefined ?  d : v

More robust case with optional param for allowing you to tell it to use some falsey values

const defaulTo = (default, ...allowed) => value =>  value === undefined || !allowed.includes(value) ?  default : value

I'm a little tired ATM so someone may want to check my allowed version

[Chalarangelo]

It is kind of weird and messes up falsey values. We either remove it entirely or refactor it into something useful. As it stands it's a bit of a mess and it's my fault for merging it.

@skatcat31 might be onto something with the first snippet in the last comment, the second one is a bit too excessive in my opinion.

[prodigic]

i like it as coalesce similar to the SQL use

const coalesce = (...args) => args.find(_ => ![NaN,undefined,null].includes(_))

or closed over a set of excluded values

const coalesce = (...excludes) => (...args) => args.find(_ => !excludes.includes(_))

[Chalarangelo]

Can you provide a quick example of how this works @prodigic? It might be worthwhile to add it in.

[skatcat31]

@Chalarangelo I agree that the second one is a bit to excessive. It was meant to be a more in depth example of something that behaved a little more like a whitelist. Realistically you should only ever default if undefined since undefined is not a lack of data, but a lack of reference:

• undefined : no reference, cannot define
• null : specifically a lack of value at reference
• NaN : it's Not a Number, this could be a valid value as it's at the reference
• false : a Boolean. In this case it's a value at the reference
• 0 : a Number. In this case it's a value at the reference
• '' : A String. In this case it's a value at the reference

So I think the first one is a little bit more along the lines of what the function describes it doing

If a value does not exist, it will return the default

Contexts are weird man

[prodigic]

coalesce(myNickName, myFullName, "");

would return the first value not filtered from the args, so if myNickName===null it return myFullName moving along the parameters til it finds the first item that passes the excludes test.

kind of works like this https://stackoverflow.com/questions/18528468/what-is-the-difference-bewteen-ifnull-and-coalesce-in-mysql except with a broader definition of excluded values.

const coalesce = (...args) => args.find(_ => ![undefined,null].includes(_))

const coalesceFactory = (...excludes = [null,undefined]) => (...args) => args.find(_ => !excludes.includes(_))

taking @skatcat31's observation and defaulting to skipping null/undefined by defualt.

[skatcat31]

@prodigic It's a cool method, but I think it's a little different than if one does not exist. coalesce is more of a filter function isn't it?

[prodigic]

yeah it does have a different goal really, I'll PR it as a separate snippet

[skatcat31]

@prodigic one last question... are you sure you want to rest and then spread it, or do it against a collection(iterables should be okay) without a rest input so that it isn't something you always have to spread too or collect for, just use an array?

[Chalarangelo]

I think we should remove value or default and stick with coalesce. It's a more robust snippet with a clear purpose and the current value or default is a little problematic. Anyone against this?

[Chalarangelo]

I am closing the issue for now as it is not about valueOrDefault anymore. The snippet will be removed as it's not really useful right now. If anyone wants to add a coalesce function, I'd be ok with that.

[skatcat31]

valueOrDefault is kind of a weird function, I'll agree. coalesce is more of a first valid which is really nice, and extremely useful in promise race conditions.

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