Opposite of nullish coalescing operator

user_356083 0
Viewed 5504

Nullish coalescing operator allows assigning a variable if it's not null or undefined, or an expression otherwise.

a = b ?? other

It is an improvement over previously used || because || will also assign other if b is empty string or other falsy, but not nullish value.

However, sometimes, we also use && for value assignment, for example

a = b && func(b)

where we only want to do func on b if it's not nullish, otherwise assign the nullish b.

Of course, && checks for falsiness, not nullishness. Is there a nullish version of &&?

nullish-coalescing typescript javascript
4 Answers
user_9061130

This will not answer the question since it was already answered by @str, I'm just posting this here because I don't have enough rep to comment on @Dalou's answer and don't want people to trip on that answer.

a = (b ?? false) && other

Is not the opposite of ??, since a will take the value of b if b is a falsy value other than undefined/null, like '' or 0 for example. The opposite of ?? should set a to the value of other even if b is '' or 0.

user_35424220

ANSWER:

let a = 9;

if( a!==null || a!==undefined ){ /* actions */ };

if( (a??null) !== null ){ /* actions */ }

PROPOSAL:

const oo = console.log;
let a; // undefined, null

// Syntax proposal: !?
a !? oo('NOT Nullish coalescing operator');

// Logical NOT Nullish assignment:
let a = 7;
a !?= 5;
oo(a); // 5

let b, c = null;
b !?= 3;
oo(b); // undefined
c !?= 8;
oo(c); // null
user_179217190

I don't like it but here's my solution:

output = typeof input === 'boolean' && "other"

Truth table:

input     -> output
--------------------
null      -> false
undefined -> false
true      -> "other"
false     -> "other"
user_109542430
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