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Refactoring to convert && chain to optional chain expression #35018
Description
interface Foo {
bar?: {
baz?: string;
}
}
declare let foo: Foo | undefined;
[|foo && foo.bar && foo.bar.baz|]It should be possible to convert that chain into the following:
interface Foo {
bar?: {
baz?: string;
}
}
declare let foo: Foo | undefined;
foo?.bar?.baz;
Activity
DanielRosenwasser commentedon Nov 9, 2019
You know, mostly like this
Urigo commentedon Nov 9, 2019
maybe a code-mode or babel transform that runs throughout a codebase?
DanielRosenwasser commentedon Nov 9, 2019
Uri Goldshtein (@Urigo) That could be done too, but I think having this granularity is good because it's not strictly the same semantics.
?.always returnsundefined,&&keeps the original nullish value.switz commentedon Nov 10, 2019
Also keep in mind that optional chaining returns
trueon0and''(empty string), normally falsy values in javascript. So running this as a code mod would almost certainly cause unintended bugs.MLoughry commentedon Nov 11, 2019
I'm not sure I really follow. Such code would be rather questionable in the first place, no? If you have an
&&chain that could be converted to an optional chain, and it returns''orfalseas a short-circuit, then the same code would be throwing a TypeError if the value is a non-empty string ortrue.fatcerberus commentedon Nov 12, 2019
I could certainly envision a scenario where code was written that depends on short-circuiting on falsy values. We're eternally stuck with
typeof null === 'object'for backward compatibility reasons, after all.Also there's no TypeError because boolean and string are object-coercible. The subsequent property access would just return
undefinedand short-circuit.jineshshah36 commentedon Nov 17, 2019
[|foo && foo.bar && foo.bar.baz|]
What do the “|” mean?
dragomirtitian commentedon Nov 18, 2019
Jinesh Shah (@jineshshah36)
[|code|]is the syntax used typescript four-slash tests to mark a selection. Some diagnostic suggestions are not exposed unless they can be applied to the selected code.MrAndersen1 commentedon Dec 9, 2019
All too eager to start using the ?. syntax I managed to play a trick on myself by converting
if (foo && foo.bar && foo.bar.indexOf(someValue) !== -1)to
if (foo?.bar?.indexOf(someValue) !== -1)which had quite the opposite behaviour of what was intended heh.
Just one of the (probably more obvious in hindsight) things a script would have to keep in mind :)
[-]Convert && chain to optional chain expression[/-][+]Refactoring to convert && chain to optional chain expression[/+]DanielRosenwasser commentedon May 5, 2020
There's a question of whether or not nullish coalescing (
??) should be supported here as part of the code action.DanielRosenwasser commentedon May 5, 2020
Also, what the supported patterns are:
&&property chains:a && a.b.c && a.b.c.da?.b.c?.da.b ? a.b.c : "hello"a.b?.c ?? "hello"cisstring | null?&&property/call chains:a && a.b.c && a.b.c()a?.b.c?.()Kingwl commentedon May 13, 2020
Ahhhh, i have some existed work about this. And I'm happy to port here
kylemh commentedon May 13, 2020
I’m not sure of the viability of going after library refactorings (as opposed to just JS -> TS), but I think one huge win would be if TS could automatically refactor lodash/get usages and/or ramda/pathOr usages.
Kingwl commentedon May 13, 2020
Good idea. IMO TypeScript cannot provide that but there's outside tools.
eg: https://github.com/HearTao/ts-upgrade
Kingwl commentedon May 20, 2020
Are there any existed tools or algorithms to compare expression and judge they are equality?
I have some ugly work about it but they cannot work well.