(I've also put this on reddit, which I've copied this from. Hope the formatting doesn't go haywire...)
First course of action for this proposal is, obviously, to
come up with a better name for it....
Motivation
As with the 'optional chaining' proposal for tc39, this operator is a way to avoid excess and annoying code from safety-checking.
The optional chaining proposal, above, follows a chain and short-circuits it upon acting on a null object, returning a safe 'undefined' result; it can be thought of as an extended 'if' sequence. It looks like this:
// safeVal = result of someProp, or undefined if looking for props on null obj
const safeVal = blah?.someMethod()?.someProp;
This proposal provides for an 'else' scenario, particularly in situations where chaining isn't appropriate, by forwarding the result of a truthy conditional check to a single-parameter function.
Syntax
condition ?! fn : expr
Parameters
- condition: any condition, identical to use in standard ternary
- fn: function taking single parameter, which is the result of evaluating condition
- expr: any _expression_, identical to use in standard ternary
Usage Example
// temporary variable
const temp = getSomething(),
foo = temp ? doSomething(temp) : doSomethingElse();
// repeated code, possible side-effects
const foo2 = getSomething() ? doSomething(getSomething()) : doSomethingElse();
// proposal, no chaining
const newFoo = getSomething() ?! x => doSomething(x) : doSomethingElse();
// proposal, chaining
const newFoo = getSomething() ?!
x => {
doSomethingFirst();
return x.doSomething();
} :
doSomethingElse();
Notes
The choice of '?!' is entirely arbitrary and not a core part of the proposal.
The result of the conditional check is not passed on to the falsey path, because it seems pointless to do so.
