TypeScript and RegExp

Question

TypeScript says:

The property ' $1 ' does not exist with a value of the type ' { (pattern: string, flags?: string): RegExp; new(pattern: string, flags?: string): RegExp; } { (pattern: string, flags?: string): RegExp; new(pattern: string, flags?: string): RegExp; } { (pattern: string, flags?: string): RegExp; new(pattern: string, flags?: string): RegExp; } '

We explain the type by looking at the definition from lib.d.ts , which appeared using TypeScript 0.8.2:

 interface RegExp { /** * Executes a search on a string using a regular expression pattern, and returns an array containing the results of that search. * @param string The String object or string literal on which to perform the search. */ exec(string: string): RegExpExecArray; /** * Returns a Boolean value that indicates whether or not a pattern exists in a searched string. * @param string String on which to perform the search. */ test(string: string): bool; /** Returns a copy of the text of the regular expression pattern. Read-only. The rgExp argument is a Regular expression object. It can be a variable name or a literal. */ source: string; /** Returns a Boolean value indicating the state of the global flag (g) used with a regular expression. Default is false. Read-only. */ global: bool; /** Returns a Boolean value indicating the state of the ignoreCase flag (i) used with a regular expression. Default is false. Read-only. */ ignoreCase: bool; /** Returns a Boolean value indicating the state of the multiline flag (m) used with a regular expression. Default is false. Read-only. */ multiline: bool; lastIndex: number; } declare var RegExp: { new (pattern: string, flags?: string): RegExp; (pattern: string, flags?: string): RegExp; } 

My question is, how can I change / update this to allow me to reference RegExp.$1 , RegExp.$2 , etc.? It is preferable that I can declare separately, since I do not intend to directly edit lib.d.ts (which will most likely be replaced as it is updated)

I tried this to no avail:

 declare var RegExp: { new (pattern: string, flags?: string): RegExp; (pattern: string, flags?: string): RegExp; $1: any; $2: any; $3: any; $4: any; $5: any; $6: any; $7: any; $8: any; $9: any; } 

I assume that they should be declared with type string . But in any case, it does not remove the error.

In addition to this, I also wonder what exactly this means (why is this declared with and without new ?):

 new (pattern: string, flags?: string): RegExp; (pattern: string, flags?: string): RegExp; 

Answer 1

Your declare var is close. Interfaces are open, so you can simply write:

 interface RegExp { $1: string; $2: string; // etc } 

Regarding the second, this is because new RegExp('[AZ]') and RegExp('[AZ]') work to create RegExp (in terms of type, this is both an invokable function and a constructor function).