Logical assignment operators in JavaScript combine Logical Operators and Assignment Expressions.
//"Or Or Equals"
x ||= y;
x || (x = y);
// "And And Equals"
x &&= y;
x && (x = y);
// "QQ Equals"
x ??= y;
x ?? (x = y);
So, say you have a function updateID it can vary in the below ways:
const updateID = user => {
// We can do this
if (!user.id) user.id = 1
// Or this
user.id = user.id || 1
// Or use logical assignment operator.
user.id ||= 1
}
You could also use it with ??
function setOpts(opts) {
opts.cat ??= 'meow'
opts.dog ??= 'bow';
}
setOpts({ cat: 'meow' })
This is on stage-4 and you should be able to use it today!
I am happy that I was able to co-champion this proposal.
7 Years ago it was just a thought!
Top comments (11)
Nice work, thank you for sharing.
I understand better the ??= example with a console.log and changing assignment here: repl
So opts.dog ??= 'bow'; means: if opts.dog is not set, assign bow
Hi! I'm not sure -- isn't x ||= y the same as x = x || y ? This is aligned to how other operators (+=, *=, etc.) do work.
x ||= 1would meanx || (x = 1)Aren't the two expressions
x = x || yandx || (x = y)equivalent?Nice work, @hemanth ! These will be super handy
Nice work on a very useful addition to the language. Great to see you stuck with it.
Very useful new features! Looks like you got the variables mixed up in the examples:
Should be
... unless I got this all wrong?
True, fixed it. I was trying to bring in another variable.
Imho, it would be important to emphasise on ??= checking for null and undefined, while ||= checking for falsy values. Could save some bugs :D
Same as:
0 || 42 // 42
0 && 42 // 0
0 ?? 42 // 0
Yup, so dev.to/hemanth/vs-2ke7
Some comments may only be visible to logged-in visitors. Sign in to view all comments.