Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?

Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?

I’ll explain by example:
Elvis Operator (?: )

The “Elvis operator” is a shortening
of Java’s ternary operator. One
instance of where this is handy is for
returning a ‘sensible default’ value
if an expression resolves to false or
null. A simple example might look like
this:

def gender = user.male ? “male” : “female” //traditional ternary operator usage

def displayName = user.name ?: “Anonymous” //more compact Elvis operator

Safe Navigation Operator (?.)
The Safe Navigation operator is used
to avoid a NullPointerException.
Typically when you have a reference to
an object you might need to verify
that it is not null before accessing
methods or properties of the object.
To avoid this, the safe navigation
operator will simply return null
instead of throwing an exception, like
so:

def user = User.find( “admin” ) //this might be null if ‘admin’ does not exist
def streetName = user?.address?.street //streetName will be null if user or user.address is null – no NPE thrown

Related:  find the time left in a setTimeout()?

Solutions/Answers:

Solution 1:

You can use the logical ‘OR’ operator in place of the Elvis operator:

For example displayname = user.name || "Anonymous" .

But Javascript currently doesn’t have the other functionality. I’d recommend looking at CoffeeScript if you want an alternative syntax. It has some shorthand that is similar to what you are looking for.

For example The Existential Operator

zip = lottery.drawWinner?().address?.zipcode

Function shortcuts

()->  // equivalent to function(){}

Sexy function calling

func 'arg1','arg2' // equivalent to func('arg1','arg2')

There is also multiline comments and classes. Obviously you have to compile this to javascript or insert into the page as <script type='text/coffeescript>' but it adds a lot of functionality 🙂 . Using <script type='text/coffeescript'> is really only intended for development and not production.

Solution 2:

I think the following is equivalent to the safe navigation operator, although a bit longer:

var streetName = user && user.address && user.address.street;

streetName will then be either the value of user.address.street or undefined.

If you want it to default to something else you can combine with the above shortcut or to give:

var streetName = (user && user.address && user.address.street) || "Unknown Street";

Solution 3:

Javascript’s logical OR operator is short-circuiting and can replace your “Elvis” operator:

var displayName = user.name || "Anonymous";

However, to my knowledge there’s no equivalent to your ?. operator.

Related:  Static variables in JavaScript

Solution 4:

I’ve occasionally found the following idiom useful:

a?.b.?c

can be rewritten as:

((a||{}).b||{}).c

This takes advantage of the fact that getting unknown attributes on an object returns undefined, rather than throwing an exception as it does on null or undefined, so we replace null and undefined with an empty object before navigating.

Solution 5:

i think lodash _.get() can help here, as in _.get(user, 'name'), and more complex tasks like _.get(o, 'a[0].b.c', 'default-value')

Solution 6:

Not yet. Maybe soon. There is currently a draft spec:

https://github.com/tc39/proposal-optional-chaining

https://tc39.github.io/proposal-optional-chaining/

For now, though, I like to use lodash get(object, path [,defaultValue]) or dlv delve(obj, keypath)