Module jsffi

This Module implements types and macros to facilitate the wrapping of, and interaction with JavaScript libraries. Using the provided types JsObject and JsAssoc together with the provided macros allows for smoother interfacing with JavaScript, allowing for example quick and easy imports of JavaScript variables:

# Here, we are using jQuery for just a few calls and do not want to wrap the
# whole library:

# import the document object and the console
var document {. importc, nodecl .}: JsObject
var console {. importc, nodecl .}: JsObject
# import the "$" function
proc jq(selector: JsObject): JsObject {. importcpp: "$(#)" .}

# Use jQuery to make the following code run, after the document is ready.
# This uses an experimental ``.()`` operator for ``JsObject``, to emit
# JavaScript calls, when no corresponding proc exists for ``JsObject``.
proc main =
  jq(document).ready(proc() =
    console.log("Hello JavaScript!")
  )

Imports

macros, tables

Types

JsObject = ref object of JsRoot

Dynamically typed wrapper around a JavaScript object.

JsAssoc[K; V] = ref object of JsRoot

Statically typed wrapper around a JavaScript object.

js = JsObject

Vars

jsArguments: JsObject

JavaScript's arguments pseudo-variable

jsNull: JsObject

JavaScript's null literal

jsUndefined: JsObject

JavaScript's undefined literal

jsDirname: cstring

JavaScript's __dirname pseudo-variable

jsFilename: cstring

JavaScript's __filename pseudo-variable

Procs

proc newJsObject(): JsObject {...}{.importcpp: "{@}".}

Creates a new empty JsObject

proc newJsAssoc[K, V](): JsAssoc[K, V] {...}{.importcpp: "{@}".}

Creates a new empty JsAssoc with key type K and value type V.

proc hasOwnProperty(x: JsObject; prop: cstring): bool {...}{.
    importcpp: "#.hasOwnProperty(#)".}

Checks, whether x has a property of name prop.

proc jsTypeOf(x: JsObject): cstring {...}{.importcpp: "typeof(#)".}

Returns the name of the JsObject's JavaScript type as a cstring.

proc jsNew(x: auto): JsObject {...}{.importcpp: "(new #)".}

Turns a regular function call into an invocation of the JavaScript's new operator

proc jsDelete(x: auto): JsObject {...}{.importcpp: "(delete #)".}

JavaScript's delete operator

proc require(module: cstring): JsObject {...}{.importc.}

JavaScript's require function

proc to(x: JsObject; T: typedesc): T:type {...}{.importcpp: "(#)".}

Converts a JsObject x to type T.

proc toJs[T](val: T): JsObject {...}{.importcpp: "(#)".}

Converts a value of any type to type JsObject

proc `&`(a, b: cstring): cstring {...}{.importcpp: "(# + #)".}

Concatenation operator for JavaScript strings

proc `+`(x, y: JsObject): JsObject {...}{.importcpp: "(# + #)".}

proc `-`(x, y: JsObject): JsObject {...}{.importcpp: "(# - #)".}

proc `*`(x, y: JsObject): JsObject {...}{.importcpp: "(# * #)".}

proc `/`(x, y: JsObject): JsObject {...}{.importcpp: "(# / #)".}

proc `%`(x, y: JsObject): JsObject {...}{.importcpp: "(# % #)".}

proc `+=`(x, y: JsObject): JsObject {...}{.importcpp: "(# += #)", discardable.}

proc `-=`(x, y: JsObject): JsObject {...}{.importcpp: "(# -= #)", discardable.}

proc `*=`(x, y: JsObject): JsObject {...}{.importcpp: "(# *= #)", discardable.}

proc `/=`(x, y: JsObject): JsObject {...}{.importcpp: "(# /= #)", discardable.}

proc `%=`(x, y: JsObject): JsObject {...}{.importcpp: "(# %= #)", discardable.}

proc `++`(x: JsObject): JsObject {...}{.importcpp: "(++#)".}

proc `--`(x: JsObject): JsObject {...}{.importcpp: "(--#)".}

proc `>`(x, y: JsObject): JsObject {...}{.importcpp: "(# > #)".}

proc `<`(x, y: JsObject): JsObject {...}{.importcpp: "(# < #)".}

proc `>=`(x, y: JsObject): JsObject {...}{.importcpp: "(# >= #)".}

proc `<=`(x, y: JsObject): JsObject {...}{.importcpp: "(# <= #)".}

proc `and`(x, y: JsObject): JsObject {...}{.importcpp: "(# && #)".}

proc `or`(x, y: JsObject): JsObject {...}{.importcpp: "(# || #)".}

proc `not`(x: JsObject): JsObject {...}{.importcpp: "(!#)".}

proc `in`(x, y: JsObject): JsObject {...}{.importcpp: "(# in #)".}

proc `[]`(obj: JsObject; field: cstring): JsObject {...}{.importcpp: "#[#]".}

Return the value of a property of name field from a JsObject obj.

proc `[]`(obj: JsObject; field: int): JsObject {...}{.importcpp: "#[#]".}

Return the value of a property of name field from a JsObject obj.

proc `[]=`[T](obj: JsObject; field: cstring; val: T) {...}{.importcpp: "#[#] = #".}

Set the value of a property of name field in a JsObject obj to v.

proc `[]=`[T](obj: JsObject; field: int; val: T) {...}{.importcpp: "#[#] = #".}

Set the value of a property of name field in a JsObject obj to v.

proc `[]`[K: not string; V](obj: JsAssoc[K, V]; field: K): V {...}{.importcpp: "#[#]".}

Return the value of a property of name field from a JsAssoc obj.

proc `[]`[V](obj: JsAssoc[string, V]; field: cstring): V {...}{.importcpp: "#[#]".}

Return the value of a property of name field from a JsAssoc obj.

proc `[]=`[K: not string; V](obj: JsAssoc[K, V]; field: K; val: V) {...}{.importcpp: "#[#] = #".}

Set the value of a property of name field in a JsAssoc obj to v.

proc `[]=`[V](obj: JsAssoc[string, V]; field: cstring; val: V) {...}{.importcpp: "#[#] = #".}

Set the value of a property of name field in a JsAssoc obj to v.

proc `==`(x, y: JsRoot): bool {...}{.importcpp: "(# === #)".}

Compare two JsObjects or JsAssocs. Be careful though, as this is comparison like in JavaScript, so if your JsObjects are in fact JavaScript Objects, and not strings or numbers, this is a comparison of references.

Iterators

iterator pairs(obj: JsObject): (cstring, JsObject) {...}{.raises: [], tags: [].}

Yields tuples of type (cstring, JsObject), with the first entry being the name of a fields in the JsObject and the second being its value wrapped into a JsObject.

iterator items(obj: JsObject): JsObject {...}{.raises: [], tags: [].}

Yields the values of each field in a JsObject, wrapped into a JsObject.

iterator keys(obj: JsObject): cstring {...}{.raises: [], tags: [].}

Yields the names of each field in a JsObject.

iterator pairs[K, V](assoc: JsAssoc[K, V]): (K, V)

Yields tuples of type (K, V), with the first entry being a key in the JsAssoc and the second being its corresponding value.

iterator items[K, V](assoc: JsAssoc[K, V]): V

Yields the values in a JsAssoc.

iterator keys[K, V](assoc: JsAssoc[K, V]): K

Yields the keys in a JsAssoc.

Macros

macro jsFromAst(n: untyped): untyped

macro `.`(obj: JsObject; field: untyped): JsObject

Experimental dot accessor (get) for type JsObject. Returns the value of a property of name field from a JsObject x.

Example:

let obj = newJsObject()
obj.a = 20
console.log(obj.a) # puts 20 onto the console.

macro `.=`(obj: JsObject; field, value: untyped): untyped

Experimental dot accessor (set) for type JsObject. Sets the value of a property of name field in a JsObject x to value.

macro `.()`(obj: JsObject; field: untyped; args: varargs[JsObject, jsFromAst]): JsObject

Experimental "method call" operator for type JsObject. Takes the name of a method of the JavaScript object (field) and calls it with args as arguments, returning a JsObject (which may be discarded, and may be undefined, if the method does not return anything, so be careful when using this.)

Example:

# Let's get back to the console example:
var console {. importc, nodecl .}: JsObject
let res = console.log("I return undefined!")
console.log(res) # This prints undefined, as console.log always returns
                 # undefined. Thus one has to be careful, when using
                 # JsObject calls.

macro `.`[K: string | cstring; V](obj: JsAssoc[K, V]; field: untyped): V

Experimental dot accessor (get) for type JsAssoc. Returns the value of a property of name field from a JsObject x.

macro `.=`[K: string | cstring; V](obj: JsAssoc[K, V]; field: untyped; value: V): untyped

Experimental dot accessor (set) for type JsAssoc. Sets the value of a property of name field in a JsObject x to value.

macro `.()`[K: string | cstring; V: proc](obj: JsAssoc[K, V]; field: untyped;
                                    args: varargs[untyped]): auto

Experimental "method call" operator for type JsAssoc. Takes the name of a method of the JavaScript object (field) and calls it with args as arguments. Here, everything is typechecked, so you do not have to worry about undefined return values.

macro `{}`(typ: typedesc; xs: varargs[untyped]): auto

Takes a typedesc as its first argument, and a series of expressions of type key: value, and returns a value of the specified type with each field key set to value, as specified in the arguments of {}.

Example:

# Let's say we have a type with a ton of fields, where some fields do not
# need to be set, and we do not want those fields to be set to ``nil``:
type
  ExtremelyHugeType = ref object
    a, b, c, d, e, f, g: int
    h, i, j, k, l: cstring
    # And even more fields ...

let obj = ExtremelyHugeType{ a: 1, k: "foo".cstring, d: 42 }

# This generates roughly the same JavaScript as:
{. emit: "var obj = {a: 1, k: "foo", d: 42};" .}

macro bindMethod(procedure: typed): auto

Takes the name of a procedure and wraps it into a lambda missing the first argument, which passes the JavaScript builtin this as the first argument to the procedure. Returns the resulting lambda.

Example:

We want to generate roughly this JavaScript:

var obj = {a: 10};
obj.someMethod = function() {
  return this.a + 42;
};

We can achieve this using the bindMethod macro:

let obj = JsObject{ a: 10 }
proc someMethodImpl(that: JsObject): int =
  that.a.to(int) + 42
obj.someMethod = bindMethod someMethodImpl

# Alternatively:
obj.someMethod = bindMethod
  proc(that: JsObject): int = that.a.to(int) + 42

Templates

template toJs(s: string): JsObject