Add JS_ThrowPlainError

It's a helper for doing the following steps:

- Building an Error object
- Attaching a formatted message
- Throwing the object

Fixes: #375

quickjs.c

@@ -6673,6 +6673,43 @@ static JSValue JS_ThrowError(JSContext *ctx, JSErrorEnum error_num,
     return JS_ThrowError2(ctx, error_num, fmt, ap, add_backtrace);
 }
 
+JSValue __attribute__((format(printf, 2, 3))) JS_ThrowPlainError(JSContext *ctx, const char *fmt, ...)
+{
+    JSRuntime *rt = ctx->rt;
+    JSStackFrame *sf;
+    BOOL add_backtrace;
+    JSValue val, ret;
+    char buf[256];
+    va_list ap;
+
+    sf = rt->current_stack_frame;
+    add_backtrace = !rt->in_out_of_memory &&
+        (!sf || (JS_GetFunctionBytecode(sf->cur_func) == NULL));
+
+    va_start(ap, fmt);
+    vsnprintf(buf, sizeof(buf), fmt, ap);
+    va_end(ap);
+
+    val = JS_NewError(ctx);
+    if (unlikely(JS_IsException(val))) {
+        /* out of memory: throw JS_NULL to avoid recursing */
+        val = JS_NULL;
+    } else {
+        JSValue msg = JS_NewString(ctx, buf);
+        if (JS_IsException(msg))
+            msg = JS_NewString(ctx, "Invalid error message");
+        if (!JS_IsException(msg)) {
+            JS_DefinePropertyValue(ctx, val, JS_ATOM_message, msg,
+                                   JS_PROP_WRITABLE | JS_PROP_CONFIGURABLE);
+        }
+    }
+    if (add_backtrace) {
+        build_backtrace(ctx, val, NULL, 0, 0, 0);
+    }
+    ret = JS_Throw(ctx, val);
+    return ret;
+}
+
 JSValue __attribute__((format(printf, 2, 3))) JS_ThrowSyntaxError(JSContext *ctx, const char *fmt, ...)
 {
     JSValue val;

quickjs.h

@@ -580,6 +580,7 @@ JS_EXTERN JSValue JS_GetException(JSContext *ctx);
 JS_EXTERN JS_BOOL JS_IsError(JSContext *ctx, JSValue val);
 JS_EXTERN void JS_ResetUncatchableError(JSContext *ctx);
 JS_EXTERN JSValue JS_NewError(JSContext *ctx);
+JS_EXTERN JSValue __js_printf_like(2, 3) JS_ThrowPlainError(JSContext *ctx, const char *fmt, ...);
 JS_EXTERN JSValue __js_printf_like(2, 3) JS_ThrowSyntaxError(JSContext *ctx, const char *fmt, ...);
 JS_EXTERN JSValue __js_printf_like(2, 3) JS_ThrowTypeError(JSContext *ctx, const char *fmt, ...);
 JS_EXTERN JSValue __js_printf_like(2, 3) JS_ThrowReferenceError(JSContext *ctx, const char *fmt, ...);