JS "JavaScript Proper"
JS modules declare and implement the JavaScript compiler, interpreter, decompiler, GC and atom manager, and standard classes.JavaScript uses untyped bytecode and runtime type tagging of data values. The jsval type is a signed machine word that contains either a signed integer value (if the low bit is set), or a type-tagged pointer or boolean value (if the low bit is clear). Tagged pointers all refer to 8-byte-aligned things in the GC heap.
Objects consist of a possibly shared structural description, called the map or scope; and unshared property values in a vector, called the slots. Object properties are associated with nonnegative integers stored in jsval′s, or with atoms (unique string descriptors) if named by an identifier or a non-integral index expression.
Scripts contain bytecode, source annotations, and a pool of string, number, and identifier literals. Functions are objects that extend scripts or native functions with formal parameters, a literal syntax, and a distinct primitive type ("function").
The compiler consists of a recursive-descent parser and a random-logic rather than table-driven lexical scanner. Semantic and lexical feedback are used to disambiguate hard cases such as missing semicolons, assignable expressions ("lvalues" in C parlance), etc. The parser generates bytecode as it parses, using fixup lists for downward branches and code buffering and rewriting for exceptional cases such as for loops. It attempts no error recovery. The interpreter executes the bytecode of top-level scripts, and calls itself indirectly to interpret function bodies (which are also scripts). All state associated with an interpreter instance is passed through formal parameters to the interpreter entry point; most implicit state is collected in a type named JSContext. Therefore, all API and almost all other functions in JSRef take a JSContext pointer as their first argument. 数据挖掘研究院
The decompiler translates postfix bytecode into infix source by consulting a separate byte-sized code, called source notes, to disambiguate bytecodes that result from more than one grammatical production.
The GC is a mark-and-sweep, non-conservative (exact) collector. It can allocate only fixed-sized things -- the current size is two machine words. It is used to hold JS object and string descriptors (but not property lists or string bytes), and double-precision floating point numbers. It runs automatically only when maxbytes (as passed to JS_NewRuntime()) bytes of GC things have been allocated and another thing-allocation request is made. JS API users should call JS_GC() or JS_MaybeGC() between script executions or from the branch callback, as often as necessary. 数据挖掘研究院
An important point about the GC′s "exactness": you must add roots for new objects created by your native methods if you store references to them into a non-JS structure in the malloc heap or in static data. Also, if you make a new object in a native method, but do not store it through the rval result parameter (see math_abs in the "Using the JS API" section above) so that it is in a known root, the object is guaranteed to survive only until another new object is created. Either lock the first new object when making two in a row, or store it in a root you′ve added, or store it via rval. See the GC tips document for more. 数据挖掘研究院
The atom manager consists of a hash table associating strings uniquely with scanner/parser information such as keyword type, index in script or function literal pool, etc. Atoms play three roles in JSRef: as literals referred to by unaligned 16-bit immediate bytecode operands, as unique string descriptors for efficient property name hashing, and as members of the root GC set for exact GC. 数据挖掘研究院
Native objects and methods for arrays, booleans, dates, functions, numbers, and strings are implemented using the JS API and certain internal interfaces used as "fast paths". 数据挖掘研究院
In general, errors are signaled by false or unoverloaded-null return values, and are reported using JS_ReportError() or one of its variants by the lowest level in order to provide the most detail. Client code can substitute its own error reporting function and suppress errors, or reflect them into Java or some other runtime system as exceptions, GUI dialogs, etc.. 数据挖掘研究院
File walk-through (OUT OF DATE!)
jsapi.c, jsapi.h
The public API to be used by almost all client code. If your client code can′t make do with jsapi.h, and must reach into a friend or private js* file, please let us know so we can extend jsapi.h to include what you need in a fashion that we can support over the long run.jspubtd.h, jsprvtd.h
These files exist to group struct and scalar typedefs so they can be used everywhere without dragging in struct definitions from N different files. The jspubtd.h file contains public typedefs, and is included by jsapi.h. The jsprvtd.h file contains private typedefs and is included by various .h files that need type names, but not type sizes or declarations.jsdbgapi.c, jsdbgapi.h
The Debugging API, still very much under development. Provided so far:- Traps, with which breakpoints, single-stepping, step over, step out, and so on can be implemented. The debugger will have to consult jsopcode.def on its own to figure out where to plant trap instructions to implement functions like step out, but a future jsdbgapi.h will provide convenience interfaces to do these things. At most one trap per bytecode can be set. When a script (JSScript) is destroyed, all traps set in its bytecode are cleared.
- Watchpoints, for intercepting set operations on properties and running a debugger-supplied function that receives the old value and a pointer to the new one, which it can use to modify the new value being set.
- Line number to PC and back mapping functions. The line-to-PC direction "rounds" toward the next bytecode generated from a line greater than or equal to the input line, and may return the PC of a for-loop update part, if given the line number of the loop body′s closing brace. Any line after the last one in a script or function maps to a PC one byte beyond the last bytecode in the script. An example, from perfect.js:
14 function perfect(n) 15 { 16 print("The perfect numbers up to " + n + " are:"); 17 18 // We build sumOfDivisors[i] to hold a string expression for 19 // the sum of the divisors of i, excluding i itself. 20 var sumOfDivisors = new ExprArray(n+1,1); 21 for (var divisor = 2; divisor <= n; divisor++) { 22 for (var j = divisor + divisor; j <= n; j += divisor) { 23 sumOfDivisors[j] += " + " + divisor; 24 } 25 // At this point everything up to ′divisor′ has its sumOfDivisors 26 // expression calculated, so we can determine whether it′s perfect 27 // already by evaluating. 28 if (eval(sumOfDivisors[divisor]) == divisor) { 29 print("" + divisor + " = " + sumOfDivisors[divisor]); 30 } 31 } 32 delete sumOfDivisors; 33 print("That′s all."); 34 }The line number to PC and back mappings can be tested using the js program with the following script:load("perfect.js") print(perfect) dis(perfect) print() for (var ln = 0; ln <= 40; ln++) { var pc = line2pc(perfect,ln) var ln2 = pc2line(perfect,pc) print(" line " + ln + " => pc " + pc + " => line " + ln2) } 数据挖掘研究院The result of the for loop over lines 0 to 40 inclusive is:line 0 => pc 0 => line 16 line 1 => pc 0 => line 16 line 2 => pc 0 => line 16 line 3 => pc 0 => line 16 line 4 => pc 0 => line 16 line 5 => pc 0 => line 16 line 6 => pc 0 => line 16 line 7 => pc 0 => line 16 line 8 => pc 0 => line 16 line 9 => pc 0 => line 16 line 10 => pc 0 => line 16 line 11 => pc 0 => line 16 line 12 => pc 0 => line 16 line 13 => pc 0 => line 16 line 14 => pc 0 => line 16 line 15 => pc 0 => line 16 line 16 => pc 0 => line 16 line 17 => pc 19 => line 20 line 18 => pc 19 => line 20 line 19 => pc 19 => line 20 line 20 => pc 19 => line 20 line 21 => pc 36 => line 21 line 22 => pc 53 => line 22 line 23 => pc 74 => line 23 line 24 => pc 92 => line 22 line 25 => pc 106 => line 28 line 26 => pc 106 => line 28 line 27 => pc 106 => line 28 line 28 => pc 106 => line 28 line 29 => pc 127 => line 29 line 30 => pc 154 => line 21 line 31 => pc 154 => line 21 line 32 => pc 161 => line 32 line 33 => pc 172 => line 33 line 34 => pc 172 => line 33 line 35 => pc 172 => line 33 line 36 => pc 172 => line 33 line 37 => pc 172 => line 33 line 38 => pc 172 => line 33 line 39 => pc 172 => line 33 line 40 => pc 172 => line 33 数据挖掘实验室
jsconfig.h
Various configuration macros defined as 0 or 1 depending on how JS_VERSION is defined (as 10 for JavaScript 1.0, 11 for JavaScript 1.1, etc.). Not all macros are tested around related code yet. In particular, JS 1.0 support is missing from JSRef. JS 1.2 support will appear in a future JSRef release.js.c
The "JS shell", a simple interpreter program that uses the JS API and more than a few internal interfaces (some of these internal interfaces could be replaced by jsapi.h calls). The js program built from this source provides a test vehicle for evaluating scripts and calling functions, trying out new debugger primitives, etc.jsarray.*, jsbool.*, jdsdate.*, jsfun.*, jsmath.*, jsnum.*, jsstr.*
These file pairs implement the standard classes and (where they exist) their underlying primitive types. They have similar structure, generally starting with class definitions and continuing with internal constructors, finalizers, and helper functions.jsobj.*, jsscope.*
These two pairs declare and implement the JS object system. All of the following happen here:- creating objects by class and prototype, and finalizing objects;
- defining, looking up, getting, setting, and deleting properties;
- creating and destroying properties and binding names to them.
