问题
I've put together a very simple program that uses JavaScriptCore to evaluate JS:
#import <CoreFoundation/CoreFoundation.h>
#import <JavaScriptCore/JavaScriptCore.h>
int main(int argc, const char * argv[])
{
JSGlobalContextRef ctx = JSGlobalContextCreate(NULL);
FILE *f = fopen(argv[1],"r");
char * buffer = malloc(10000000);
fread(buffer,1,10000000,f);
CFStringRef strs = CFStringCreateWithCString(NULL, buffer, kCFStringEncodingASCII);
JSStringRef jsstr = JSStringCreateWithCFString(strs);
JSValueRef result = JSEvaluateScript(ctx, jsstr, NULL, NULL, 0, NULL);
double res = JSValueToNumber(ctx, result, NULL);
JSGlobalContextRelease(ctx);
printf("%lf\n", res);
return 0;
}
The idea here is that the last value is expected to be a Number
, and that value is printed. This works for valid javascript code, such as
var square = function(x) { return x*x; }; square(4)
However, if the code tries to perform a console.log
, the program segfaults. Is there a log function available in JSC or do I have to roll my own?
回答1:
You do have to provide your own console log if using the JavaScriptCore framework from Mac or IOS.
Here is some code that worked for me (sorry it is Objective-C rather than standard C as per your code above):
JSContext *javascriptContext = [[JSContext alloc] init];
javascriptContext[@"consoleLog"] = ^(NSString *message) {
NSLog(@"Javascript log: %@",message);
};
Then you use it from Javascript by:
consoleLog("My debug message");
Note that I have tried to define a vararg version (log taking multiple parameters) but I couldn't get this to work correctly across the framework api.
Note that this solution uses features introduced with the new Objective-C API for the JavaScriptCore.framework introduced at the same time as IOS 7. If you are looking for an intro to this well-integrated bridge between Objective-C and Javascript, check out the 2013 WWDC introduction "Integrating JavaScript into Native Apps" session on Apple's developer network: https://developer.apple.com/videos/wwdc/2013/?id=615
Update to answer:
For those of you wanting to maximise your javascript code reuse without refactoring, I've managed to get a version working that declares a log of the form console.log() :
JSContext *javascriptContext = [[JSContext alloc] init];
[javascriptContext evaluateScript:@"var console = {}"];
javascriptContext[@"console"][@"log"] = ^(NSString *message) {
NSLog(@"Javascript log: %@",message);
};
Then you use it from Javascript by:
console.log("My debug message");
回答2:
Swift 3.0
let javascriptContext = JSContext()
javascriptContext?.evaluateScript("var console = { log: function(message) { _consoleLog(message) } }")
let consoleLog: @convention(block) (String) -> Void = { message in
print("console.log: " + message)
}
javascriptContext?.setObject(unsafeBitCast(consoleLog, to: AnyObject.self), forKeyedSubscript: "_consoleLog" as (NSCopying & NSObjectProtocol)!)
Swift 2.1
let javascriptContext = JSContext()
javascriptContext.evaluateScript("var console = { log: function(message) { _consoleLog(message) } }")
let consoleLog: @convention(block) String -> Void = { message in
print("console.log: " + message)
}
javascriptContext.setObject(unsafeBitCast(consoleLog, AnyObject.self), forKeyedSubscript: "_consoleLog")
Then you use it from Javascript by:
console.log("My debug message");
回答3:
self.jsContext = JSContext()
self.jsContext.evaluateScript(...)
let logFunction: @convention(block) (String) -> Void = { (string: String) in
print(string)
}
self.jsContext.setObject(logFunction, forKeyedSubscript: "consoleLog" as NSCopying & NSObjectProtocol)
回答4:
You can debug JS file attached to context in Safari.
Steps:
1) Start Safari
2) In Safari, enable the Develop menu by going to "Preferences" -> "Advanced" -> "Show Develop menu in menu bar"
3) Go to Develop menu -> "Simulator" or name of your computer -> select "Automatically show web inspector for JSContexts" and "Automatically pause connecting to JSContexts"
4) Re-run your project and Safari should auto-show the web inspector
来源:https://stackoverflow.com/questions/19649932/javascriptcore-console-log