dbl = JS_NewDouble(cx, (jsdouble)v);
jsdouble d; LL_L2D(d, v); dbl = JS_NewDouble(cx, d);
JAM_DOUBLE(JSContext *cx, double v, jsdouble *dbl){   dbl = JS_NewDouble(cx, (jsdouble)v);   return DOUBLE_TO_JSVAL(dbl);}