Js_re

Provide bindings to JS regular expressions (RegExp).

Note: This is not an immutable API. A RegExp object with the global ("g") flag set will modify the lastIndex property when the RegExp object is used, and subsequent uses will continue the search from the previous lastIndex.

t

type t

The RegExp object.

result

type result

The result of a executing a RegExp on a string.

captures

let captures: result => array<Js.nullable<string>>

An array of the match and captures, the first is the full match and the remaining are the substring captures.

matches

let matches: result => array<string>

Deprecated. Use captures instead.

index

let index: result => int

0-based index of the match in the input string.

input

let input: result => string

The original input string.

fromString

let fromString: string => t

Constructs a RegExp object (Js.Re.t) from a string. Regex literals %re("/.../") should generally be preferred, but fromString is useful when you need to dynamically construct a regex using strings, exactly like when you do so in JavaScript.

RES
let firstReScriptFileExtension = (filename, content) => {
  let result = Js.Re.fromString(filename ++ "\.(res|resi)")->Js.Re.exec_(content)
  switch result {
  | Some(r) => Js.Nullable.toOption(Js.Re.captures(r)[1])
  | None => None
  }
}

// outputs "res"
firstReScriptFileExtension("School", "School.res School.resi Main.js School.bs.js")

fromStringWithFlags

let fromStringWithFlags: (string, ~flags: string) => t

Constructs a RegExp object (Js.Re.t) from a string with the given flags. See Js.Re.fromString.

Valid flags:

• g global

• i ignore case

• m multiline

• u unicode (es2015)

• y sticky (es2015)

flags

let flags: t => string

Returns the enabled flags as a string.

global

let global: t => bool

Returns a bool indicating whether the global flag is set.

ignoreCase

let ignoreCase: t => bool

Returns a bool indicating whether the ignoreCase flag is set.

lastIndex

let lastIndex: t => int

Returns the index where the next match will start its search. This property will be modified when the RegExp object is used, if the global ("g") flag is set.

RES
let re = %re("/ab*TODO/g")
let str = "abbcdefabh"

let break = ref(false)
while !break.contents {
  switch Js.Re.exec_(re, str) {
  | Some(result) => Js.Nullable.iter(Js.Re.captures(result)[0], (. match_) => {
      let next = Belt.Int.toString(Js.Re.lastIndex(re))
      Js.log("Found " ++ (match_ ++ (". Next match starts at " ++ next)))
    })
  | None => break := true
  }
}

See RegExp: lastIndex on MDN.

setLastIndex

let setLastIndex: (t, int) => unit

Sets the index at which the next match will start its search from.

multiline

let multiline: t => bool

Returns a bool indicating whether the multiline flag is set.

source

let source: t => string

Returns the pattern as a string.

sticky

let sticky: t => bool

Returns a bool indicating whether the sticky flag is set.

unicode

let unicode: t => bool

Returns a bool indicating whether the unicode flag is set.

exec_

let exec_: (t, string) => option<result>

Executes a search on a given string using the given RegExp object. Returns Some(Js.Re.result) if a match is found, None otherwise.

RES
/* Match "quick brown" followed by "jumps", ignoring characters in between
 * Remember "brown" and "jumps"
 * Ignore case
 */

let re = %re("/quick\s(brown).+?(jumps)/ig")
let result = Js.Re.exec_(re, "The Quick Brown Fox Jumps Over The Lazy Dog")

See RegExp.prototype.exec() on MDN.

test_

let test_: (t, string) => bool

Tests whether the given RegExp object will match a given string. Returns true if a match is found, false otherwise.

RES
/* A simple implementation of Js.String.startsWith */

let str = "hello world!"

let startsWith = (target, substring) =>
  Js.Re.fromString("^" ++ substring)->Js.Re.test_(target)

Js.log(str->startsWith("hello")) /* prints "true" */

See RegExp.prototype.test() on MDN.