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Overloads for String.prototype.split method #61816
Description
⚙ Compilation target
ES2020
⚙ Library
lib.es5.d.ts
Missing / Incorrect Definition
It is not wrong definition, but if it is possible, I would like to suggest add overloads for String.prototype.split method
I like to use string template types instead of just string as much as possible, and it works like a charm. The problem is that when I try to split my well-known string, it returns just string[] type which isn't very descriptive
My suggestion is to add simple overloads:
- When the
separatorisstringandlimitis not provided orundefined - When the
separatorisstring | RegExpandlimitis0
I added zero to the list because it is straightforward to implement that case, but if it means that I also should provide type checking for negative values, noninteger values and correct tuple splitting type then forget about it 😁
We can completely remove limit from overloads. I added it just to get the same type for provided limit as undefined and not provided limit otherwise the return type will be string[] if the value of limit is undefined
Sample Code
type Split<Source extends string, Separator extends string> = Source extends `${infer Left}${Separator}${infer Right}`
? [...(string extends Left ? string[] : [`${Left}`]), ...Split<Right, Separator>]
: Source extends ""
? Separator extends ""
? []
: [""]
: string extends Source
? string[]
: [Source];
interface String {
split<Source extends string, Separator extends string>(
this: Source,
separator: Separator,
limit?: undefined,
): Split<Source, Separator>;
split(separator: string | RegExp, limit: 0): [];
}You can see types in action on playground (with examples)
Documentation Link
No response
Activity
MartinJohns commentedon Jun 4, 2025
Duplicate of #56333 / #53362.
EzioMercer commentedon Jun 4, 2025
Martin Johns (@MartinJohns) Ryan Cavanaugh (@RyanCavanaugh) I don't think that it is a duplicate because in mentioned (and other) issues a lot of cases didn't handled. Please look at playground link which I provided
EzioMercer commentedon Jun 5, 2025
Ryan Cavanaugh (@RyanCavanaugh) Please give it a chance. I really did my best to write these overloads. I covered a lot of edge cases. I gave about 20 cases that I could think of, but if there are uncovered edge cases that don't work, please feel free to add them in the comments, I'll try to handle them too.
MartinJohns commentedon Jun 5, 2025
It's still a duplicate. Another approach doesn't justify a new issue. You can add your suggestion in the open issue, which is still labelled as "Awaiting More Feedback".
Also this comment is relevant: #53362 (comment)
Your suggestion is extremely complex for a corner case and requires the addition of a new utility type (potentially causing conflicts with user code). See also No New Utility Types.
EzioMercer commentedon Jun 5, 2025
Martin Johns (@MartinJohns) I simplified a little my type. I am not a genius of
TypeScriptso may be someone can come up with less complex definition.I will. Thank you for noticing that
UnsafeSplitTypeOnlyForStringCasesInStringSplitMethodor etc.I can't quite understand this. Don't we want to give the user as much information as possible? I understand that it's almost impossible to do everywhere, but why not where it's not that hard?
typescript-bot commentedon Jun 8, 2025
This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.