JS::CallArgs
syntax js::callargs js::callargsfromvp(unsigned argc, js::value *vp); name type description args unsigned number of argument.
...(3nd argument of jsnative) methods methods of js::callargs method description bool requireatleast(jscontext *cx, const char *fnname, unsigned required) returns true if there are at least required arguments passed in.
... methods inherited from js::callargsbase method description unsigned length() const returns the number of arguments..
...And 8 more matches

JSNative
full documentation of how to define a jsnative (or a jsfastnative, the equivalent typedef which preceded it) is available in the api header "js/callargs.h" added in spidermonkey 24.
... the preferred way to implement a function is to use the js::callargs structure defined there; the macros providing equivalent functionality are deprecated.
... the behavior of a jsnative is implemented using a js::callargs structure added in spidermonkey 17.
...And 3 more matches

Index
29 js::callargs jsapi reference, reference, référence(2), spidermonkey js::callargs is helper class encapsulating access to the callee, this value, arguments, and argument count for a function call.
... full documentation of how to define a jsnative (or a jsfastnative, the equivalent typedef which preceded it) is available in the api header "js/callargs.h" added in spidermonkey 24.
... the preferred way to implement a function is to use the js::callargs structure defined there; the macros providing equivalent functionality are deprecated.

JSAPI Cookbook
but in a jsnative the correct way to do this is: /* jsapi */ bool mynative(jscontext *cx, unsigned argc, js::value *vp) { js::callargs args = js::callargsfromvp(argc, vp); jsobject *global = js_getglobalforobject(cx, &args.callee()); ...
... } defining a function // javascript function justforfun() { return null; } /* jsapi */ bool justforfun(jscontext *cx, unsigned argc, js::value *vp) { js::callargs args = js::callargsfromvp(argc, vp); args.rval().setnull(); return true; } ...
... */ js::callargs args = js::callargsfromvp(argc, vp); args.rval().setint32(23); return true; returning a floating-point number // javascript return 3.14159; /* jsapi */ js::callargs args = js::callargsfromvp(argc, vp); args.rval().setdouble(3.14159); exception handling throw the most common idiom is to create a new error object and throw that.

JS_InstanceOf
syntax bool js_instanceof(jscontext *cx, js::handle<jsobject*> obj, const jsclass *clasp, js::callargs *args); // added in spidermonkey 38 bool js_instanceof(jscontext *cx, js::handle<jsobject*> obj, const jsclass *clasp, jsval *argv); // obsolete since jsapi 32 name type description cx jscontext * pointer to a js context from which to derive runtime information.
... args js::callargs * optional pointer to arguments.
...to use it this way, pass the arguments provided by the engine for args with js::callargsfromvp(argc, vp).

Hacking Tips
$ gdb --args out/dist/bin/js ./foo.js […] spidermonkey unwinder is disabled by default, to enable it type: enable unwinder .* spidermonkey (gdb) b js::math_cos (gdb) run […] #0 js::math_cos (cx=0x14f2640, argc=1, vp=0x7fffffff6a88) at js/src/jsmath.cpp:338 338 callargs args = callargsfromvp(argc, vp); (gdb) enable unwinder .* spidermonkey (gdb) backtrace 10 #0 0x0000000000f89979 in js::math_cos(jscontext*, unsigned int, js::value*) (cx=0x14f2640, argc=1, vp=0x7fffffff6a88) at js/src/jsmath.cpp:338 #1 0x0000000000ca9c6e in js::calljsnative(jscontext*, bool (*)(jscontext*, unsigned int, js::value*), js::callargs const&) (cx=0x14f2640, native=0xf89960 , args=...
...) at js/src/jscntxtinlines.h:235 #2 0x0000000000c87625 in js::invoke(jscontext*, js::callargs const&, js::maybeconstruct) (cx=0x14f2640, args=..., construct=js::no_construct) at js/src/vm/interpreter.cpp:476 #3 0x000000000069bdcf in js::jit::docallfallback(jscontext*, js::jit::baselineframe*, js::jit::iccall_fallback*, uint32_t, js::value*, js::mutablehandlevalue) (cx=0x14f2640, frame=0x7fffffff6ad8, stub_=0x1798838, argc=1, vp=0x7fffffff6a88, res=jsval_void) at js/src/jit/baselineic.cpp:6113 #4 0x00007ffff7f41395 in <<jitframe_exit>> () #5 0x00007ffff7f42223 in <<jitframe_baselinestub>> () #6 0x00007ffff7f4423d in <<jitframe_baselinejs>> () #7 0x00007ffff7f4222e in <<jitframe_baselinestub>> () #8 0x00007ffff7f4326a in <<jitframe_baselinejs>> () #9 0x00007ffff7f38d5f in <<jitframe_entry>> ...

JS::GetFirstArgumentAsTypeHint
syntax bool js::getfirstargumentastypehint(jscontext* cx, callargs args, jstype *result); name type description cx jscontext * the context in which to define functions.
... fs callargs the arguments of the function call.

JS::HandleValueArray
syntax js::handlevaluearray(const js::rootedvalue& value); js::handlevaluearray(const js::autovaluevector& values); js::handlevaluearray(const js::autovaluearray<n>& values); js::handlevaluearray(const js::callargs& args); js::handlevaluearray::frommarkedlocation(size_t len, const js::value *elements); js::handlevaluearray::subarray(const js::handlevaluearray& values, size_t startindex, size_t len); js::handlevaluearray::empty(); name type description value js::rootedvalue &amp; an element of newly created 1-length array.
... args js::callargs &amp; elements of newly created array.

JS::PersistentRooted
// js::persistentrootedvalue persistentval; static bool setpersistent(jscontext* cx, unsigned argc, js::value* vp) { js::callargs args = callargsfromvp(argc, vp); // set persistent value.
... persistentval.ref() = args.get(0); // or // *persistentval = args.get(0); // [spidermonkey 38] // persistentval = args.get(0); args.rval().setundefined(); return true; } static bool getpersistent(jscontext* cx, unsigned argc, js::value* vp) { js::callargs args = callargsfromvp(argc, vp); // get persistent value.

JS_ConvertArguments
syntax bool js_convertarguments(jscontext *cx, const js::callargs &args, const char *format, ...); // added in spidermonkey 31 bool js_convertarguments(jscontext *cx, unsigned argc, jsval *argv, const char *format, ...); // obsolete since jsapi 30 name type description cx jscontext * the context in which to perform any necessary conversions.
... args const js::callargs &amp; reference to the arguments to convert.

JS_ConvertArgumentsVA
syntax bool js_convertargumentsva(jscontext *cx, const js::callargs &args, const char *format, va_list ap); bool js_convertargumentsva(jscontext *cx, unsigned argc, jsval *argv, const char *format, va_list ap); name type description cx jscontext * pointer to a js context from which to derive runtime information.
... args const js::callargs &amp; reference to the arguments to convert.

JS_GetInstancePrivate
syntax void * js_getinstanceprivate(jscontext *cx, js::handle<jsobject*> obj, const jsclass *clasp, js::callargs *args); // added in jsapi 32 void * js_getinstanceprivate(jscontext *cx, js::handle<jsobject*> obj, const jsclass *clasp, jsval *argv); // obsolete since jsapi 32 name type description cx jscontext * a context.
... args js::callargs * optional argument, used for error reporting.

JS_NewObjectForConstructor
syntax jsobject * js_newobjectforconstructor(jscontext *cx, const jsclass *clasp, const js::callargs& args); // added in jsapi 32 jsobject * js_newobjectforconstructor(jscontext *cx, jsclass *clasp, const jsval *vp); // added in jsapi 14, obsolete since jsapi 32 jsobject * js_newobjectforconstructor(jscontext *cx, const jsval *vp); // obsolete since jsapi 14 name type description cx jscontext * the context in which to create the new object.
... args js::callargs &amp; call argument to get a constructor as callee.

How to embed the JavaScript engine
static bool doit(jscontext *cx, unsigned argc, jsval *vp) { js::callargs args = callargsfromvp(argc, vp); /* * look in argv for argc actual parameters, set *rval to return a * value to the caller.

JSClass
_finalize }; /* spidermonkey 31 or older * static jsclass printer_class = { * "printer", * jsclass_has_private, * js_propertystub, js_propertystub, js_propertystub, js_strictpropertystub, * js_enumeratestub, js_resolvestub, js_convertstub, printer_finalize, * jsclass_no_optional_members * }; */ bool printer_construct(jscontext *cx, unsigned argc, jsval *vp) { js::callargs args = js::callargsfromvp(argc, vp); jsobject *obj = js_newobjectforconstructor(cx, &printer_class, args); /* spidermonkey 31 or older * jsobject *obj = js_newobjectforconstructor(cx, &printer_class, vp); */ if (!obj) return false; myprinter *p = new myprinter; if (p == null) { js_reportoutofmemory(cx); return false; } js_setprivate(c...