JS::Value
js::value is the type of javascript values in the jsapi. a c++ variable of type js::value represents a value in javascript: a string, number, object (including arrays and functions), boolean, symbol, null, or undefined. js::value is a class whose internal structure is an implementation detail. embeddings should not rely on observed representation details or upon the size of js::value. ...
...e is the type of javascript values in the jsapi. a c++ variable of type js::value represents a value in javascript: a string, number, object (including arrays and functions), boolean, symbol, null, or undefined. js::value is a class whose internal structure is an implementation detail. embeddings should not rely on observed representation details or upon the size of js::value. ...
...:value represents a value in javascript: a string, number, object (including arrays and functions), boolean, symbol, null, or undefined. js::value is a class whose internal structure is an implementation detail. embeddings should not rely on observed representation details or upon the size of js::value. ...
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Index
destructor by calling js_destroyidarray. 24 js::autosaveexceptionstate jsapi reference, reference, référence(2), spidermonkey js::autosaveexceptionstate saves and later restores the current exception state of a given jscontext. 25 js::autovaluearray jsapi reference, reference, référence(2), spidermonkey js::autovaluearray<n> holds a rooted array of js::value. this is typically used for local variables being passed to function which requires js::handlevaluearray or a pointer to js::value array. 26 js::autovectorrooter jsapi reference, reference, référence(2), spidermonkey js::autovectorrooter<t> holds a variable-size rooted array of type t. 27 js::booleanvalue jsapi reference, reference, référence(2), spidermonk...
... 28 js::call jsapi reference, reference, spidermonkey js::call calls a specified function, fun, on an object, thisobj. in terms of function execution, the object is treated as this. ...
...caller must either ensure dst has enough space to encode the entire string, or pass the length of the buffer as dstlenp. in which case, the function will encode characters from the string until the buffer is exhausted. does not write the null terminator. 39 js::doublenanvalue jsapi reference, reference, référence(2), spidermonkey js::doublenanvalue returns a value of type js::value that represents an ieee floating-point quiet not-a-number (nan). 40 js::doublevalue jsapi reference, reference, référence(2), spidermonkey js::doublevalue converts a c floating-point number of type double to js::value, the type of javascript values. 41 js::evaluate jsapi reference, reference, référence(2), spidermonkey js::evaluate compiles and execut...
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WebIDL bindings
a readonly attribute only has a getter and no setter. the getter's name is the name of the attribute...
...a readonly attribute only has a getter and no setter. the getter's name is the name of the attribute with the first letter converted to uppercase. this has get prepended to it if any of these conditions hold: the type of the at...
...st represented by the argument type itself, set to the default value if the argument was not in fact passed in. variadic webidl arguments are treated as a const sequence<>& around the actual argument type. here's a table, see the specific sections below for more details and explanations. ...
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GC Rooting Guide
api user. since spidermonkey has a moving gc, it is very important that it knows about each and every pointer to a gc thing in the system. spidermonkey's rooting api tries to make this task as simple as possible. what is a gc thing pointer? "gc thing" is the term used to refer to memory allocated and managed by the spidermonkey garbage collector. the main types of gc thing pointer are: js::value jsobject* jsstring* jsscript* jsid note that js::value and jsid can contain pointers internally even though they are not a normal pointer type, hence their inclusion in this list. if you use these types directly, or create classes, structs or arrays that contain them, you must follow the rules set out in this guide. if you do not your program will not work correctly - if it works at all. ...
...::rooted<t> instance behaves exactly as if it were the underlying pointer. js::rooted must be constructed with a jscontext*, and optionally an initial value. there are typedefs available for the main types. ...
...ot free (though it only costs a few cycles). thus, it makes more sense to only root the gc thing once and reuse it through an indirect reference. like a reference, a js::handle is immutable: it can only ever refer to the js::rooted<t> that it was created for. similarly to js::rooted<t>, there are typedefs available for the main types: template class typedef js::handle<js::value> js::handlevalue js::handle<jsobject*> js::handleobject js::handle<jsstring*> js::handlestring js::handle<jsscript*> js::handlescript js::handle<jsid> js::handleid you should use js::handle<t> for all function parameters taking gc thing pointers (except out-parameters, which are described below). for example, instead of: jsobject * somef...
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JSAPI Cookbook
this article shows the jsapi equivalent for a tiny handful of common javascript idioms. note: the foss wiki page contains a few links to other libraries and programs that can make life easier when using spidermonkey and jsapi. basics working with values the basic, undifferentiated value type in the jsapi is js::value. to query whether a value has a particular type, use a correspondingly named member testing function: // javascript var v = computesomevalue(); var isstring = typeof v === "string"; var isnumber = typeof v === "number"; var isnull = v === null; var isboolean = typeof v === "boolean"; var isobject = typeof v === "object" && v !== null; /* jsapi */ js::rootedvalue v(cx, computesomevalue()); bool isstring = v.isstring(); bool isnumber = v.isnumber(); bool isint32 = v.isint32()...
...: v = js::booleanvalue(false); finding the global object many of these recipes require finding the current global object first. // javascript var global = this; there is a function, js_getglobalforscopechain(cx), that makes a best guess, and sometimes that is the best that can be done. 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; } ... ...
...tion /* jsapi * * suppose the script defines a global javascript * function foo() and we want to call it from c. */ js::rootedvalue r(cx); if (!js_callfunctionname(cx, js_getglobalobject(cx), "foo", 0, null, &r)) return false; calling a js function via a local variable // javascript var r = f(); // where f is a local variable /* jsapi * * suppose f is a local c variable of type js::value. */ js::autovaluevector args(cx); // empty argument list js::rootedvalue r(cx); if (!js_callfunctionvalue(cx, null, f, args, &r) return false; returning an integer // javascript return 23; /* jsapi * * warning: this only works for integers that fit in 32 bits. * otherwise, convert the number to floating point (see the next example). */ js::callargs args = js::callargsfromvp(argc, v...
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JSAPI User Guide
as the global object can call them, just as any web page can call alert. in the environment we have created, the "hello world" script looks like this: system("echo hello world"); jsapi concepts this section aims to fill in the major gaps in the picture of the jsapi presented so far. to do anything useful with spidermonkey, you must read all three sections. ...
...ented so far. to do anything useful with spidermonkey, you must read all three sections. javascript values main article: js::value javascript is a dynamically typed language: variables and properties do not have a type that is fixed at compile time. how can a statically typed language, like c or c++, in which all variables have types, interact with javascript? the jsapi provides a data type, js::value (also with a deprecated jsval typedef), which can contain javascript values of any type. a js::value can be a number, a string, a boolean value, a reference to an object (like an object, array, date, or function), or one of the special values null or undefined. for integers and boolean values, a jsval contains the value itself. in other cases, the jsval is a pointer to an object, string, or numb...
...ipt values of any type. a js::value can be a number, a string, a boolean value, a reference to an object (like an object, array, date, or function), or one of the special values null or undefined. for integers and boolean values, a jsval contains the value itself. in other cases, the jsval is a pointer to an object, string, or number. warning: like c++ pointers, and unlike javascript vars, a js::value is not automatically initialized to a safe value, and can become a dangling pointer! a dangling pointer is a pointer that used to point to a valid object, but no longer does because the object no longer exists. using a dangling pointer can crash a c++ program (or worse). in the case of js::value, the javascript garbage collector recycles objects, strings, and numbers that don't appear to be in u...
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JS::Add*Root
s discouraged since it could be removed at any time. try to avoid using it. this article covers features introduced in spidermonkey 31 register a variable as a member of the garbage collector's root set, to protect anything the root points at from garbage collection. these functions are obsoleted, use js::persistentrooted instead. ...
...s root set, to protect anything the root points at from garbage collection. these functions are obsoleted, use js::persistentrooted instead. ...
... js::persistentrooted instead. ...
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JS_GetPositiveInfinityValue
js_getnegativeinfinityvalue returns the corresponding negative infinity. ...
...js_getnegativeinfinityvalue returns the corresponding negative infinity. ...
...js_getnegativeinfinityvalue returns the corresponding negative infinity. ...
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JS::CallArgs
this article covers features introduced in spidermonkey 17 helper class encapsulating access to the callee, this value, arguments, and argument count for a function call. syntax js::callargs js::callargsfromvp(unsigned argc, js::value *vp); name type description args unsigned number of argument. (2nd argument of jsnative) vp js::value * a pointer to the argument value array. (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. if false, it reports an error message on the context. methods inherited from js::callargsbase method ...
... returns the function being called, as a value. must not be called after rval() has been used! js::handlevalue thisv() const returns the this value passed to the function. this method must not be called when the function is being called as a constructor via new. the value may or may not be an object: it is the individual function's responsibility to box the value if needed. js::value computethis(jscontext *cx) const returns the this value if this is an object, otherwise calls js_computethis and returns it. bool isconstructing() const returns true if the function is called via new. mutablehandlevalue rval() const returns the currently-set return value. the initial contents of this value are unspecified. once this method has been called, callee()...
...' signatures but won't require invasive changes to the methods' implementations, potentially under time pressure. js::callargs encapsulates access to the callee, this, the function call's arguments, and eventual return value for a function call. the principal way to create a callargs is like so, using js::callargsfromvp: static bool functionreturningargctimesarg0(jscontext *cx, unsigned argc, js::value *vp) { js::callargs args = js::callargsfromvp(argc, vp); // guard against no arguments or a non-numeric arg0. if (args.length() == 0 || !args[0].isnumber()) { args.rval().setint32(0); return true; } // access to the callee must occur before accessing/setting // the return value. jsobject &callee = rec.callee(); // it's always fine to access thisv...

JS::DoubleNaNValue
this article covers features introduced in spidermonkey 24 create a not-a-number (nan) floating-point number as a value of type js::value. syntax js::value js::doublenanvalue() description js::doublenanvalue returns a value of type js::value that represents an ieee floating-point quiet not-a-number (nan). ...
... this article covers features introduced in spidermonkey 24 create a not-a-number (nan) floating-point number as a value of type js::value. syntax js::value js::doublenanvalue() description js::doublenanvalue returns a value of type js::value that represents an ieee floating-point quiet not-a-number (nan). ...
...covers features introduced in spidermonkey 24 create a not-a-number (nan) floating-point number as a value of type js::value. syntax js::value js::doublenanvalue() description js::doublenanvalue returns a value of type js::value that represents an ieee floating-point quiet not-a-number (nan). ...

JS::Remove*Root
me browsers, its use is discouraged since it could be removed at any time. try to avoid using it. this article covers features introduced in spidermonkey 31 unregister a pointer to a gc thing so that it is no longer a member of the garbage collector's root set. this enables any pointed-at gc thing to be garbage collected as needed. ...
... root set. this enables any pointed-at gc thing to be garbage collected as needed. syntax void removevalueroot(jscontext *cx, js::heap<js::value> *vp); void removestringroot(jscontext *cx, js::heap<jsstring *> *rp); void removeobjectroot(jscontext *cx, js::heap<jsobject *> *rp); void removescriptroot(jscontext *cx, js::heap<jsscript *> *rp); void removevaluerootrt(jsruntime *rt, js::heap<js::value> *vp); void removestringrootrt(jsruntime *rt, js::heap<jsstring *> *rp); void removeobjectrootrt(jsruntime *rt, js::heap<jsobject *> *rp); void removescriptrootrt(jsruntime *rt, js::heap<jsscript *> *rp); name type description cx jscontext * the context from which to remove the root. requires request. in a js_threadsafe build, the caller must be in a request on ...
...js::heap<jsobject *> *rp); void removescriptrootrt(jsruntime *rt, js::heap<jsscript *> *rp); name type description cx jscontext * the context from which to remove the root. requires request. in a js_threadsafe build, the caller must be in a request on this jscontext. rt jsruntime * the runtime from which to remove the root. vp js::heap<js::value> address of the js::value variable to remove from the root set. this must have been passed to one of js::addvalueroot, js::addnamedvalueroot or js::addnamedvaluerootrt. rp js::heap<jsstring *> address of the jsstring * variable to remove from the root set. this must have been passed to either js::addstringroot or js::addnamedstringroot. rp js::heap<jsobject *> add...

JS_GetNaNValue
nan is typically used in javascript as the return value of a numeric operation when an argument is invalid or conversion fails. for example, 0/0 and math.sqrt(-1) both return nan. so do number("xyzzy") and math.sin("frank"). ...
... nan is typically used in javascript as the return value of a numeric operation when an argument is invalid or conversion fails. for example, 0/0 and math.sqrt(-1) both return nan. so do number("xyzzy") and math.sin("frank"). ...
... and math.sin("frank"). ...

JS_GetReservedSlot
access an object's reserved slots. syntax // added in spidermonkey 42 js::value js_getreservedslot(jsobject *obj, uint32_t index); void js_setreservedslot(jsobject *obj, uint32_t index, js::value v); // obsolete since spidermonkey 42 jsval js_getreservedslot(jsobject *obj, uint32_t index); void js_setreservedslot(jsobject *obj, uint32_t index, jsval v); name type description obj jsobject * an object that has reserved slots. index uint32_t index of the reserved slot to access. v js::value (in js_setreservedslot) the value to store. description if a jsclass has jsclass_has_reserved_slots(n) in its flags, with n > 0, or has a non-null jsclass.reserveslots callback, then objects of that class have n reserved slots in which ...
... reserved slots may also contain private values to store pointer values (whose lowest bit is 0) or uint32_t, when non-javascript values must be stored; the garbage collector ignores such values when it sees them. ...
...t not be exposed directly to javascript. it's only legal to store and retrieve data from private values. they cannot be returned from functions, set as properties on objects, embedded in javascript arrays, and so on.) new objects' reserved slots are initialized to undefined. see also mxr id search for js_getreservedslot mxr id search for js_setreservedslot bug 1184564 -- changed jsval to js::value ...

JS_NumberValue
this article covers features introduced in spidermonkey 17 convert a c floating-point number of type double to a js::value. replacement to js_newnumbervalue, js_newdoublevalue, js_newdouble. syntax // added in spidermonkey 42 js::value js_numbervalue(double d); // obsolete since spidermonkey 42 jsval js_numbervalue(double d); name type description d double the numeric value to convert. description js_numbervalue converts a c floating-point number of type double to js::value, the type of javascript values. the result is an integer js::value if d can be stored that way. ...
...double d); // obsolete since spidermonkey 42 jsval js_numbervalue(double d); name type description d double the numeric value to convert. ...
...ion d double the numeric value to convert. description js_numbervalue converts a c floating-point number of type double to js::value, the type of javascript values. the result is an integer js::value if d can be stored that way. ...

JS_SameValue
rict equality (===) in that +0 and -0 are not the same and in that nan is the same as nan. the samevalue algorithm is equivalent to the following javascript: function samevalue(v1, v2) { if (v1 === 0 && v2 === 0) return 1 / v1 === 1 / v2; if (v1 !== v1 && v2 !== v2) return true; return v1 === v2; } syntax // added in spidermonkey 45 bool js_samevalue(jscontext *cx, js::handle<js::value> v1, js::handle<js::value> v2, bool *same); // obsolete since jsapi 39 bool js_samevalue(jscontext *cx, jsval v1, jsval v2, bool *same); name type description cx jscontext * pointer to a js context from which to derive runtime information. requires request. in a js_threadsafe build, the caller must be in a request on this jscontext. v1 js...
... description js_samevalue determines whether two values are the same, returning true or false accordingly. this method is infallible. ...
... bool js_samevalue(jscontext *cx, jsval v1, jsval v2, bool *same); name type description cx jscontext * pointer to a js context from which to derive runtime information. requires request. in a js_threadsafe build, the caller must be in a request on this jscontext. v1 js::handle&lt;js::value&gt; / jsval the first value. v2 js::handle&lt;js::value&gt; / jsval the second value. description js_samevalue determines whether two values are the same, returning true or false accordingly. this method is infallible. see also mxr id search for js_samevalue js_strictlyequal js_looselyequal bug 1132045 -- use handle ...