Starting up
/*
* Tune this to avoid wasting space for shallow stacks, while saving on
* malloc overhead/fragmentation for deep or highly-variable stacks.
*/
#define STACK_CHUNK_SIZE 8192
JSRuntime *rt;
JSContext *cx;
/* You need a runtime and one or more contexts to do anything with JS. */
rt = JS_NewRuntime(0x400000L);
if (!rt)
fail("can′t create JavaScript runtime");
cx = JS_NewContext(rt, STACK_CHUNK_SIZE);
if (!cx)
fail("can′t create JavaScript context");
/*
* The context definitely wants a global object, in order to have standard
* classes and functions like Date and parseInt. See below for details on
* JS_NewObject.
*/
JSObject *globalObj;
globalObj = JS_NewObject(cx, &my_global_class, 0, 0);
JS_InitStandardClasses(cx, globalObj); 数据挖掘实验室
Defining objects and properties
/* Statically initialize a class to make "one-off" objects. */
JSClass my_class = {
"MyClass",
/* All of these can be replaced with the corresponding JS_*Stub
function pointers. */
my_addProperty, my_delProperty, my_getProperty, my_setProperty,
my_enumerate, my_resolve, my_convert, my_finalize
};
JSObject *obj;
/*
* Define an object named in the global scope that can be enumerated by
* for/in loops. The parent object is passed as the second argument, as
* with all other API calls that take an object/name pair. The prototype
* passed in is null, so the default object prototype will be used.
*/
obj = JS_DefineObject(cx, globalObj, "myObject", &my_class, NULL,
JSPROP_ENUMERATE);
/*
* Define a bunch of properties with a JSPropertySpec array statically
* initialized and terminated with a null-name entry. Besides its name,
* each property has a "tiny" identifier (MY_COLOR, e.g.) that can be used
* in switch statements (in a common my_getProperty function, for example).
*/
enum my_tinyid {
MY_COLOR, MY_HEIGHT, MY_WIDTH, MY_FUNNY, MY_ARRAY, MY_RDONLY
};
static JSPropertySpec my_props[] = {
{"color", MY_COLOR, JSPROP_ENUMERATE},
{"height", MY_HEIGHT, JSPROP_ENUMERATE},
{"width", MY_WIDTH, JSPROP_ENUMERATE},
{"funny", MY_FUNNY, JSPROP_ENUMERATE},
{"array", MY_ARRAY, JSPROP_ENUMERATE},
{"rdonly", MY_RDONLY, JSPROP_READONLY},
{0}
};
JS_DefineProperties(cx, obj, my_props);
/*
* Given the above definitions and call to JS_DefineProperties, obj will
* need this sort of "getter" method in its class (my_class, above). See
* the example for the "It" class in js.c.
*/
static JSBool
my_getProperty(JSContext *cx, JSObject *obj, jsval id, jsval *vp)
{
if (JSVAL_IS_INT(id)) {
switch (JSVAL_TO_INT(id)) {
case MY_COLOR: *vp = . . .; break;
case MY_HEIGHT: *vp = . . .; break;
case MY_WIDTH: *vp = . . .; break;
case MY_FUNNY: *vp = . . .; break;
case MY_ARRAY: *vp = . . .; break;
case MY_RDONLY: *vp = . . .; break;
}
}
return JS_TRUE;
} 数据挖掘研究院
Defining functions
/* Define a bunch of native functions first: */
static JSBool
my_abs(JSContext *cx, JSObject *obj, uintN argc, jsval *argv, jsval *rval)
{
jsdouble x, z;
if (!JS_ValueToNumber(cx, argv[0], &x))
return JS_FALSE;
z = (x < 0) ? -x : x;
return JS_NewDoubleValue(cx, z, rval);
}
. . .
/*
* Use a JSFunctionSpec array terminated with a null name to define a
* bunch of native functions.
*/
static JSFunctionSpec my_functions[] = {
/* name native nargs */
{"abs", my_abs, 1},
{"acos", my_acos, 1},
{"asin", my_asin, 1},
. . .
{0}
};
/*
* Pass a particular object to define methods for it alone. If you pass
* a prototype object, the methods will apply to all instances past and
* future of the prototype′s class (see below for classes).
*/
JS_DefineFunctions(cx, globalObj, my_functions); 数据挖掘实验室
Defining classes
/*
* This pulls together the above API elements by defining a constructor
* function, a prototype object, and properties of the prototype and of
* the constructor, all with one API call.
*
* Initialize a class by defining its constructor function, prototype, and
* per-instance and per-class properties. The latter are called "static"
* below by analogy to Java. They are defined in the constructor object′s
* scope, so that ′MyClass.myStaticProp′ works along with ′new MyClass()′.
*
* JS_InitClass takes a lot of arguments, but you can pass null for any of
* the last four if there are no such properties or methods.
*
* Note that you do not need to call JS_InitClass to make a new instance of
* that class -- otherwise there would be a chicken-and-egg problem making
* the global object -- but you should call JS_InitClass if you require a
* constructor function for script authors to call via new, and/or a class
* prototype object (′MyClass.prototype′) for authors to extend with new
* properties at run-time. In general, if you want to support multiple
* instances that share behavior, use JS_InitClass.
*/
protoObj = JS_InitClass(cx, globalObj, NULL, &my_class,
/* native constructor function and min arg count */
MyClass, 0,
/* prototype object properties and methods -- these
will be "inherited" by all instances through
delegation up the instance′s prototype link. */
my_props, my_methods,
/* class constructor properties and methods */
my_static_props, my_static_methods); 数据挖掘实验室
Running scripts
/* These should indicate source location for diagnostics. */
char *filename;
uintN lineno;
/*
* The return value comes back here -- if it could be a GC thing, you must
* add it to the GC′s "root set" with JS_AddRoot(cx, &thing) where thing
* is a JSString *, JSObject *, or jsdouble *, and remove the root before
* rval goes out of scope, or when rval is no longer needed.
*/
jsval rval;
JSBool ok;
/*
* Some example source in a C string. Larger, non-null-terminated buffers
* can be used, if you pass the buffer length to JS_EvaluateScript.
*/
char *source = "x * f(y)";
ok = JS_EvaluateScript(cx, globalObj, source, strlen(source),
filename, lineno, &rval);
if (ok) {
/* Should get a number back from the example source. */
jsdouble d;
ok = JS_ValueToNumber(cx, rval, &d);
. . .
} 数据挖掘实验室
Calling functions
/* Call a global function named "foo" that takes no arguments. */
ok = JS_CallFunctionName(cx, globalObj, "foo", 0, 0, &rval);
jsval argv[2];
/* Call a function in obj′s scope named "method", passing two arguments. */
argv[0] = . . .;
argv[1] = . . .;
ok = JS_CallFunctionName(cx, obj, "method", 2, argv, &rval);
Shutting down
/* For each context you′ve created: */
JS_DestroyContext(cx);
/* For each runtime: */
JS_DestroyRuntime(rt);
/* And finally: */
JS_ShutDown(); 数据挖掘研究院
Debugging API
See the
trap, untrap, watch, unwatch, line2pc, and
pc2line commands in
js.c. Also the (scant) comments in
jsdbgapi.h.
