From iPhone Development Wiki
Jump to: navigation, search
Cydia Package
Developer saurik
Package ID cycript
Latest Version 0.9.594

Cycript is a JavaScript interpreter which also understands Objective-C syntax. The cycript binary is also a REPL for this language.

Besides evaluating scripts, Cycript can also hook into a running process (using cycript -p process) and modify its property.

Official documentation can be found on

Presentations about Cycript: saurik explaining how to use Cycript on OS X, targeting the iOS simulator; Adam Bell explaining how to use Cycript to prototype a tweak (example code).

JS/ObjC Object Bridging

Some native JavaScript types are bridged to the corresponding Objective-C types for convenient, so you can use

[[41,"foo",true,[8,6],{a:12,b:46},36] indexOfObject:"foo"]

instead of

[[NSArray arrayWithObjects:
  [NSNumber numberWithInt:41],
  [NSNumber numberWithBool:YES],
  [NSArray arrayWithObjects:[NSNumber numberWithInt:8], [NSNumber numberWithInt:6], nil],
  [NSDictionary dictionaryWithObjectsAndKeys:
    [NSNumber numberWithInt:12], "a",
    [NSNumber numberWithInt:46], "b",
  [NSNumber numberWithInt:36],
nil] indexOfObject:"foo"]
JS type ObjC type
number NSNumber (CFNumber)
boolean NSNumber (CFBoolean)
string NSString
Array NSArray
object (Associative array) NSDictionary

null in Cycript is equivalent to nil in Objective-C. Additionally, nil, YES and NO are also defined in Cycript.

JavaScript 1.6+ Features

Cycript supports the following JavaScript 1.6+ features extended by Mozilla:

Additional syntax

New Syntax Meaning "Desugared" representation
[obj msg:var] Sends msg to obj with parameters var. This is the Objective-C's message sending syntax. objc_msgSend(obj, @selector(msg).value, var ...)
@import(module) Import a .cy file. Similar to JavaScript's require() function.
@selector(selname) Returns the selector named selname with Objective-C syntax. new Selector("selname");
obj->ivar Obtain the instant variable ivar of an Objective-C object obj. obj.$cyi.ivar
*ptr Dereference the pointer, or list all ivars of an object (so that you can access them using (*obj).ivar). ptr.$cyi
obj->[key] Equivalent to (*obj)[key].
&var Takes the address of a variable. Only instances of ObjC class can have addresses. var.$cya()
@class classname : superclass {}
methodname { function body }
methodname { function body }
Declare an Objective-C class. The classname can be omitted, where an anonymous class will be declared.
@class existingclass
methodname { function body }
methodname { function body }
Insert extra methods to an existing class. The existingclass itself can be an expression e.g. @class ([obj class]) ....
new classname Although not exactly a new syntax, this construction has a new meaning for Objective-C classes. This is similar to [classname alloc], but the resource will be managed by JavaScriptCore's garbage collector. To fully initialize the class, you need to call [new classname initWithFoo:...].
@"str" Equivalent to "str".
[super ...] A local variable representing the superclass. objc_msgSend(???, ... )
0bxxxxxx Binary literal.

REPL-only additions

These are used for debugging.

Line Usage
?debug Toggles debug output.
?bypass Bypass syntax error pretty-printing.
?expand Toggles whether to display the line break characters, etc. as really a line break or just \n.
?gc Force a JavaScript garbage collection.
?syntax Toggle syntax highlighting.

Additional types

Type/Constructor Usage
Selector(selname) Declare a selector.
Functor(function body, type encoding) Associate an Objective-C type encoding to a function, e.g. new Functor(function(x,y){return (x+y).toString(16);}, "*dd"); to declare a (double, double) → char* function.
Pointer(address, type encoding) Treat the input number as a pointer. Like C pointers, the result can be dereferenced using * and subscripted using [i], but pointer arithmetic is not directly supported.
Type(type encoding) Create a type. The resulting value can be new-ed to get a Pointer, e.g. var p = new new Type("d");. To deallocate the pointer, use the free() function.
Instance(address) Treat the address as an instance of Objective-C object.
Super(self, selector) Returns an object which, when being sent a message, will be forwarded to self's superclass.

Additionally, the identifiers like int, id, char, double, etc. are predefined to the corresponding types (new Type("i"), etc). Therefore, to allocator a pointer you may simply use new int or even new int[42].

Additional variables and methods

Variable Meaning
_ Last evaluated value (REPL only).
ObjectiveC.images An associative array, with keys beings the path of loaded libraries, and value is the classes of this library.
ObjectiveC.classes An associative array of classes. The keys are class names and the values are the classes themselves.
ObjectiveC.protocols An associative array of protocols. The keys are protocol names and the values are the protocols themselves.
obj.toJSON() Convert the object to JSON.
obj.toCYON() Convert the object to CYON (Cycript object notation).
obj.value For some objects, returns the address.
class.messages Contains an associative array of messages in the class. The keys are the selector names and the values are implementations (functions).
system.print(string) Print the string to syslog.
system.args Parameters of the executable
selector.type(class) Returns the type encoding for the selector in class. For example, @selector(copyWithZone:).type(NSString) returns @12@0:4^{_NSZone=}8.

Other uses

The cycript binary can be used to "compile" Cycript into standard JavaScript 1.5 with the -c flag, e.g.

Your-iPhone:~ mobile$ echo "[x*x for each(x in [1,2,3])]" | cycript -c > x.js
Your-iPhone:~ mobile$ cat x.js
(function($cyv,x){$cyv=[];(function($cys){$cys=[1,2,3];for(x in $cys){x=$cys[x];$cyv.push(x*x)}})();return $cyv})()


  • Every command typed into the console is run in an autorelease pool so variables "declared" in one command might be deallocated by the time the next command that uses it is run.

See also

External links