Function substringBefore

substringBefore<T extends string | null = null>(
    s: Nullish,
    delimiter: string | RegExp,
    on_missing?: T,
): T
Returns the substring before the first occurrence of the delimiter.
Type Parameters
- T extends string | null = null
Parameters
- s: Nullish
  Input string, null, or undefined.
- delimiter: string | RegExp
  String or regex marking where to end.
- Optionalon_missing: T
  Returned if s is nullish or delimiter not found (default: null).
Returns T
The substring before the delimiter, or on_missing.
Remarks
A delimiter at the beginning, including an empty string delimiter, returns an empty string rather than on_missing. Useful for extracting a path or field prefix. Regex flags are preserved; matching starts at zero without reading or changing the caller's lastIndex. Global regexes use the first match; sticky regexes must match at zero.
Example
```
substringBefore("path/to/file.txt", '/');     // "path"
substringBefore("abc123xyz", /\d+/);          // "abc"
substringBefore(undefined, ':');              // null
substringBefore("no-needle", ':', 'default'); // 'default'
```
- Defined in string/substring.ts:62
substringBefore<T extends string | null = null>(
    s: Nullable<string>,
    delimiter: string | RegExp,
    on_missing?: T,
): string | T
Returns the substring before the first occurrence of the delimiter.
Type Parameters
- T extends string | null = null
Parameters
- s: Nullable<string>
  Input string, null, or undefined.
- delimiter: string | RegExp
  String or regex marking where to end.
- Optionalon_missing: T
  Returned if s is nullish or delimiter not found (default: null).
Returns string | T
The substring before the delimiter, or on_missing.
Remarks
A delimiter at the beginning, including an empty string delimiter, returns an empty string rather than on_missing. Useful for extracting a path or field prefix. Regex flags are preserved; matching starts at zero without reading or changing the caller's lastIndex. Global regexes use the first match; sticky regexes must match at zero.
Example
```
substringBefore("path/to/file.txt", '/');     // "path"
substringBefore("abc123xyz", /\d+/);          // "abc"
substringBefore(undefined, ':');              // null
substringBefore("no-needle", ':', 'default'); // 'default'
```
- Defined in string/substring.ts:63

Function substringBefore

Type Parameters

Parameters

Returns T

Remarks

Example

Type Parameters

Parameters

Returns string | T

Remarks

Example

Settings