Command line interpreter and REPL for JSCocoa

A few months ago I started working on a JavaScript to Objective-C bridge. We had already implemented Objective-C in JavaScript, so I figured “why not?”

Well, I never got very far, but thankfully Patrick Geiller apparently had the same idea and actually executed it: He announced JSCocoa today. It looks like it’s a solid bridge, about up to par with PyObjC and RubyCocoa.

While the included GUI interface for trying out JSCocoa is nice, I prefer command line interfaces for my languages, so I ripped out the few lines of code from my original bridge and plugged in JSCocoa.

Code and build instructions on GitHub.

It’s very bare bones at the moment: it will either read one or more file names from the command line arguments, or if no arguments are supplied it will present a no-frills REPL. Obviously line-editing, etc would be one of the next steps, but for now it works nicely with rlwrap.

#import <Foundation/Foundation.h>
#import "JSCocoaController.h"

void JSValuePrint(JSContextRef, JSValueRef, JSValueRef *);

int main (int argc, const char * argv[])
    [[NSAutoreleasePool alloc] init];
    id c = [JSCocoaController sharedController];
    JSGlobalContextRef ctx = [c ctx];
    if (argc > 1)
        for (int i = 1; i < argc; i++)
            [c evalJSFile:[NSString stringWithFormat:@"%s", argv[i]]];
        while (1)
            char buffer[1024];
            printf("js> ");
            if (fgets(buffer, 1024, stdin) == NULL)
            JSStringRef script = JSStringCreateWithUTF8CString(buffer);
            JSValueRef exception = NULL;
            if (JSCheckScriptSyntax(ctx, script, 0, 0, &exception) && !exception)
                JSValueRef value = JSEvaluateScript(ctx, script, 0, 0, 0, &exception);
                if (exception)
                    JSValuePrint(ctx, exception, NULL);
                if (value && !JSValueIsUndefined(ctx, value))
                    JSValuePrint(ctx, value, &exception);
                printf("Syntax error\n");

void JSValuePrint(
                  JSContextRef ctx,
                  JSValueRef value,
                  JSValueRef *exception)
    JSStringRef string = JSValueToStringCopy(ctx, value, exception);
    size_t length = JSStringGetLength(string);
    char *buffer = malloc(length+1);
    JSStringGetUTF8CString(string, buffer, length+1);