JS_Eval single line and multi-line evaluation differs

[dbalabka]

I've found that JS_Eval evaluate some scripts differently. For example, there are two scripts:

1.  globalThis.__test= "OK";
   

2.  console.log();
    globalThis.__test= "OK";
   

The first script will executed, and globalThis.__test will be set as expected. However, the second script will not set the globalThis.__test, and there is no difference in what mode will be used, GLOBAL or MODULE. How properly should I use JS_Eval to evaluate the second script? What is the right way to use public API for this?

During my investigation, I found that qjs script evaluation implementation is quite complicated:

quickjs/qjs.c

Lines 117 to 133 in 670492d

	if ((eval_flags & JS_EVAL_TYPE_MASK) == JS_EVAL_TYPE_MODULE) {
	/* for the modules, we compile then run to be able to set
	import.meta */
	val = JS_Eval(ctx, buf, buf_len, filename,
	eval_flags | JS_EVAL_FLAG_COMPILE_ONLY);
	if (!JS_IsException(val)) {
	// ex. "<cmdline>" pr "/dev/stdin"
	use_realpath =
	!(*filename == '<' || !strncmp(filename, "/dev/", 5));
	if (js_module_set_import_meta(ctx, val, use_realpath, true) < 0) {
	js_std_dump_error(ctx);
	ret = -1;
	goto end;
	}
	val = JS_EvalFunction(ctx, val);
	}
	val = js_std_await(ctx, val);

[saghul]

If you are using quickjs as a library note that it does not include console, that is added by quickjs-libc so u less you are using that the problem is likely that you are getting an exception.

[dbalabka]

Thanks for the quick reply. Strangely, the JS_Value tag does not say that an exception occurred.

[dbalabka]

@saghul, you were right! I wrote proper polyfill to avoid the issue. Thank you a lot. Seems I don't perform a proper exception handling. Need to find out where I'm doing it wrong.

Here is a polyfill for other:

// Ensure console object exists safely
if (typeof globalThis.console === "undefined") {
    globalThis.console = {};
}

// Polyfill each console method safely
const methods = ['log', 'warn', 'error', 'info', 'debug'];
for (let method of methods) {
    if (typeof globalThis.console[method] !== 'function') {
        globalThis.console[method] = globalThis.console.log || function () {};
    }
}

// Handle console.assert separately, to mimic behavior
if (typeof globalThis.console.assert !== 'function') {
    globalThis.console.assert = function (assertion, ...args) {
        if (!assertion) {
            globalThis.console.log('Assertion failed:', ...args);
        }
    };
}