Question

我已经在外部JavaScript文件sample.js中用JavaScript编写了一个函数。例如：

function getNum()
{
    return 123;
}

是否可以使用JavaScriptCore从C调用getNum函数？如果可以，怎么办？

我可以使用以下步骤从JavaScript函数中调用C函数“ HelloCallback”：

JSObjectRef globalObject = JSContextGetGlobalObject(global_context);
JSStringRef helloFunctionName = JSStringCreateWithUTF8CString("hello");
// make function object
JSObjectRef functionObject = JSObjectMakeFunctionWithCallback( 
                      global_context, helloFunctionName, &HelloCallback);

// set it as proprty of global object

JSObjectSetProperty(global_context,globalObject,
        helloFunctionName,functionObject,kJSPropertyAttributeNone, NULL );

 // make javascript(using sample.js file)
 JSStringRef statement = JSStringCreateWithUTF8CString("/home/amit/Desktop/sampleWebkitgtkExample/sample.js");

// evaluate it
JSEvaluateScript( global_context,statement,NULL,NULL,1, NULL );

C函数“ HelloCallback”在C文件中的定义如下：

JSValueRef HelloCallback( JSContextRef ctx             
                    , JSObjectRef function         
                    , JSObjectRef thisObject       
                    , size_t argumentCount         
                    , const JSValueRef arguments[] 
                    , JSValueRef* exception)       {
// here do the C++ stuff
printf("\nHello from C function\n");

return JSValueMakeUndefined(ctx);}

sample.js文件包含以下示例代码：

function getnum()
{
    return 123;
}
hello(); // calling C function

因此，如果我想从C调用getnum（）函数，那我们该怎么做呢？

我确实是这样的：

JSStringRef statement = JSStringCreateWithUTF8CString("/home/amit/Desktop/sampleWebkitgtkExample/sample.js");
JSEvaluateScript( global_context,statement,NULL,NULL,1, NULL );
JSStringRef script1 = JSStringCreateWithUTF8CString("getnum()");
JSValueRef x = JSEvaluateScript(global_context, script1, NULL, NULL, 0,  NULL);
printf("\n value = %d \n",x);

但是我没有得到返回的值。我在哪里出错了？

我确实喜欢这样，现在我可以调用getnum函数并获取返回的值：

char* scriptUTF8 = createStringWithContentsOfFile("/home/amit/Desktop/sampleWebkitgtkExample/sample.js");
JSStringRef script = JSStringCreateWithUTF8CString(scriptUTF8);
JSValueRef  result = JSEvaluateScript(global_context, script, NULL, NULL, 1, &exception);
if (JSValueIsUndefined(global_context, result))
     printf("PASS: Test script executed successfully.\n");
else {
         printf("FAIL: Test script returned unexcpected value:\n");
         JSStringRef exceptionIString = JSValueToStringCopy(global_context, 
                                                 exception, NULL);           
         JSStringRelease(exceptionIString);
      }

JSStringRef script1 = JSStringCreateWithUTF8CString("getnum()");
JSValueRef x = JSEvaluateScript(global_context, script1, NULL, NULL, 1,  NULL);
printf("\nvalue = %f \n",JSValueToNumber(global_context,x,NULL));

createStringWithContentsOfFile函数的定义如下：

static char* createStringWithContentsOfFile(const char* fileName)
    {
        char* buffer;       
        size_t buffer_size = 0;
        size_t buffer_capacity = 1024;
        buffer = (char*)malloc(buffer_capacity);        
        FILE* f = fopen(fileName, "r");
        if (!f) {
                     fprintf(stderr, "Could not open file: %s\n", fileName);
                     return 0;
                }

        while (!feof(f) && !ferror(f)) {
        buffer_size += fread(buffer + buffer_size, 1, buffer_capacity - 
                                                           buffer_size, f);
        if (buffer_size == buffer_capacity) { // guarantees space for 
            trailing '\0'
            buffer_capacity *= 2;
            buffer = (char*)realloc(buffer, buffer_capacity);
            assert(buffer);
        }

        assert(buffer_size < buffer_capacity);
                  }
    fclose(f);
    buffer[buffer_size] = '\0';     
    return buffer;  }

使用JavaScriptCore从C调用JavaScript函数

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