Execute Javascript in iOS Applications

In this tutorial, I have covered How to execute JavaScript in iOS / Objective-C. You can execute JavaScript in iOS applications with the help of JavaScriptCore.framework. This framework is supported in iOS7 & OSX 10.9

List of features supported by Javascript.framework
a) Evaluate JavaScript code in Objective-C
b) Access JavaScript Variables in Objective-C
c) Access JavaScript functions and execute them in Objective-C
d) Execute Objective-C code from JavaScript
e) Export Objective-C classes and use them in JavaScript.

Download the source code:

To access JavaScript framework, you need to include the header file

1	`#import <JavaScriptCore/JavaScriptCore.h>`

List of Main Classes supported by framework:
JSContext : For any javascript operations you need JSContext.

1	`JSContext` `*context = [[JSContext` `alloc]` `init];`

JSValue : JSValue holds JavaScript values,variables and functions. List of main methods in JSValue.

// Convert this value to a corresponding Objective-C object, according to the
// conversion specified above.

- (id)toObject;
 
// Convert this value to a corresponding Objective-C object, if the result is
// not of the specified class then nil will be returned.

- (id)toObjectOfClass:(Class)expectedClass;
 
// The value is copied to a boolean according to the conversion specified by the
// JavaScript language.

- (BOOL)toBool;
 
// The value is copied to a number according to the conversion specified by the
// JavaScript language.

- (double)toDouble;
 
// The value is copied to an integer according to the conversion specified by
// the JavaScript language.

- (int32_t)toInt32;
 
// The value is copied to an integer according to the conversion specified by
// the JavaScript language.

- (uint32_t)toUInt32;
 
// If the value is a boolean, a NSNumber value of @YES or @NO will be returned.
// For all other types the value will be copied to a number according to the
// conversion specified by the JavaScript language.

- (NSNumber *)toNumber;
 
// The value is copied to a string according to the conversion specified by the
// JavaScript language.

- (NSString *)toString;
 
// The value is converted to a number representing a time interval since 1970,
// and a new NSDate instance is returned.

- (NSDate *)toDate;
 
// If the value is null or undefined then nil is returned.
// If the value is not an object then a JavaScript TypeError will be thrown.
// The property "length" is read from the object, converted to an unsigned
// integer, and an NSArray of this size is allocated. Properties corresponding
// to indicies within the array bounds will be copied to the array, with
// Objective-C objects converted to equivalent JSValues as specified.

- (NSArray *)toArray;
 
// If the value is null or undefined then nil is returned.
// If the value is not an object then a JavaScript TypeError will be thrown.
// All enumerable properties of the object are copied to the dictionary, with
// Objective-C objects converted to equivalent JSValues as specified.

- (NSDictionary *)toDictionary;

Accessing Javascript Code in Objective-C

1).Evaluating Javascript Code

NSString * jsCode = @"1+2";

JSContext *context = [[JSContext alloc] init];

JSValue * value = [context evaluateScript:jsCode];

NSLog(@"Output = %d", [value toInt32]);

2).Access Javascript Variables. Variables and functions are accessed from JSContext.
To access varible from Javascript : context[@"x"]
To access function from javascript : context[@"myfun"]

JSContext *context = [[JSContext alloc] init];

    NSString * jsCode = @"var x; x=10;";

    [context evaluateScript:jsCode];
 
    JSValue * a =context[@"x"];

    NSLog(@"x = %d", [a toInt32]);

3).Access Javascript functions and execute them in Objective-C

//function with arguments

    JSContext *context = [[JSContext alloc] init];

    NSString * jsCode = @"function sum(a,b) { return a+b;} ";

    [context evaluateScript:jsCode];
 
    JSValue * func =context[@"sum"];

    NSArray * args = @[[NSNumber numberWithInt:10],[NSNumber numberWithInt:20]];

    JSValue * ret =[func callWithArguments:args];

    NSLog(@"10+20 = %d", [ret toInt32]);
 
    //function without arguments

    NSString * jsCode2 = @"function getRandom() { return parseInt(Math.floor((Math.random()*100)+1));} ";

    [context evaluateScript:jsCode2];
 
    JSValue * func2 =context[@"getRandom"];
 
    for(int i=0;i<5;i++)

    {

        JSValue * ret2 =[func2 callWithArguments:nil];

        NSLog(@"Random Value = %d", [ret2 toInt32]);

    }

Call Objective-C code from JavaScript

Objective-C code is called from JavaScript in two ways

1.CODE BLOCKS

Objective-C code block can be called from JavaScript.

JSContext *context = [[JSContext alloc] init];
 
    //we are telling that "sum" is function, takes two arguments

    context[@"sum"] = ^(int arg1,int arg2)

    {

        return arg1+arg2;

    };
 
    NSString * jsCode =@"sum(4,5);";

    JSValue * sumVal = [context evaluateScript:jsCode];
 
    NSLog(@"Sum(4,5) = %d", [sumVal toInt32]);
 
    //we are telling that "getRandom" is function, does not take any arguments

    context[@"getRandom"] = ^()

    {

        return rand()%100;

    };
 
    NSString * jsCode2 =@"getRandom();";

    for(int i=0;i<5;i++)

    {

        JSValue * sumVal2 = [context evaluateScript:jsCode2];

        NSLog(@"Random Number = %d", [sumVal2 toInt32]);

    }

2.USING JSEXPORT PROTOCOL

You can see the comparison between Objective-C Object and it’s equivalent Javascript Object below.

@interface MyObject

@property  int x;
 
-(int) getX;

+(MyObject *) getSqure:(MyObject*)obj;
 
@end
 
//Usage:

MyObject * obj = [MyObject new];

[obj getX];

[MyObject getSqure:obj];

function MyObject()
{

    //member variable

    this.x=0;
 
    //instance method

    this.getX = function() 

                    { 

                    return this.x;

                    }
}
 
//static method

MyObject.getSqure = function(obj)
{

    var newObj = new MyObject();

    newObj.x = obj.x * obj.x;

    return newObj;
}
 
//Usage: 

var obj = new MyObject();
obj.x=10;

var sqrObj = MyObject.getSqure(obj);

To make Javascript interacting with Objective-C Object, We need to have a Protocol which should be inherited
from JSExport. Move all the variables and functions to prototype to access them in JavaScript.

@protocol MyObjectExport

@property  int x;
 
-(int) getX;

+(MyObject *) getSqure:(MyObject*)obj;
 
@end
 
@interface MyObject :NSObject <MyObjectExport>
 
//this method is not accessible in javascript

-(void) test;
 
@end;
 
@implementation MyObject

@synthesize x;
 
-(int) getX
{

    return self.x;
}

+(MyObject *) getSqure:(MyObject*)obj;
{

    NSLog(@"Calling getSqure");

    MyObject * newObj = [MyObject new];

    newObj.x = obj.x * obj.x;
 
    return  newObj;
}

Now MyObject(Objective-C)’s variables and functions are directly accessed from javascript.

JSContext * context = [[JSContext alloc] init];

NSString * jsCode = @"function sqrtOf(obj){ return MyObject.getSqure(obj);}";
 
    //adding Objective-C Class to Javascript.

    context[@"MyObject"]=[MyObject class];
 
    [context evaluateScript:jsCode];
 
    MyObject * obj =[MyObject new];

    obj.x =10;
 
    JSValue * func =context[@"sqrtOf"];

    JSValue * val = [func callWithArguments:@[obj]];
 
    //we got MyObject from javascript.

    MyObject *sqrtObj = [val toObject];
 
    NSLog(@"Value =%d, %d", obj.x, [sqrtObj getX]);

转：http://hayageek.com/execute-javascript-in-ios/