The Tor Browser: js/src/doc/Debugger/Debugger.Script.md@6474c204b198 (annotated)

js/src/doc/Debugger/Debugger.Script.md@6474c204b198 (annotated)

js/src/doc/Debugger/Debugger.Script.md

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 # Debugger.Script
 A `Debugger.Script` instance refers to a sequence of bytecode in the
 debuggee; it is the [`Debugger`][debugger-object] API's presentation of a JSAPI `JSScript`
 object. Each of the following is represented by single JSScript object:
 * The body of a function—that is, all the code in the function that is not
   contained within some nested function.
 * The code passed to a single call to `eval`, excluding the bodies of any
   functions that code defines.
 * The contents of a `<script>` element.
 * A DOM event handler, whether embedded in HTML or attached to the element
   by other JavaScript code.
 * Code appearing in a `javascript:` URL.
 The [`Debugger`][debugger-object] interface constructs `Debugger.Script` objects as scripts
 of debuggee code are uncovered by the debugger: via the `onNewScript`
 handler method; via [`Debugger.Frame`][frame]'s `script` properties; via the
 `functionScript` method of [`Debugger.Object`][object] instances; and so on. For a
 given [`Debugger`][debugger-object] instance, SpiderMonkey constructs exactly one
 `Debugger.Script` instance for each underlying script object; debugger
 code can add its own properties to a script object and expect to find
 them later, use `==` to decide whether two expressions refer to the same
 script, and so on.
 (If more than one [`Debugger`][debugger-object] instance is debugging the same code, each
 [`Debugger`][debugger-object] gets a separate `Debugger.Script` instance for a given
 script. This allows the code using each [`Debugger`][debugger-object] instance to place
 whatever properties it likes on its `Debugger.Script` instances, without
 worrying about interfering with other debuggers.)
 A `Debugger.Script` instance is a strong reference to a JSScript object;
 it protects the script it refers to from being garbage collected.
 Note that SpiderMonkey may use the same `Debugger.Script` instances for
 equivalent functions or evaluated code—that is, scripts representing the
 same source code, at the same position in the same source file,
 evaluated in the same lexical environment.
 ## Accessor Properties of the Debugger.Script Prototype Object
 A `Debugger.Script` instance inherits the following accessor properties
 from its prototype:
 `url`
 :   The filename or URL from which this script's code was loaded. If the
     `source` property is non-`null`, then this is equal to `source.url`.
 `startLine`
 :   The number of the line at which this script's code starts, within the
     file or document named by `url`.
 `lineCount`
 :   The number of lines this script's code occupies, within the file or
     document named by `url`.
 `source`
 :   The [`Debugger.Source`][source] instance representing the source code from which
     this script was produced. This is `null` if the source code was not
     retained.
 `sourceStart`
 :   The character within the [`Debugger.Source`][source] instance given by `source` at
     which this script's code starts; zero-based. If this is a function's
     script, this is the index of the start of the `function` token in the
     source code.
 `sourceLength`
 :   The length, in characters, of this script's code within the
     [`Debugger.Source`][source] instance given by `source`.
 `global`
 :   A [`Debugger.Object`][object] instance referring to the global object in whose
     scope this script runs. The result refers to the global directly, not
     via a wrapper or a `WindowProxy` ("outer window", in Firefox).
 `staticLevel`
 :   The number of function bodies enclosing this script's code.
     Global code is at level zero; bodies of functions defined at the top
     level in global code are at level one; bodies of functions nested within
     those are at level two; and so on.
     A script for code passed to direct `eval` is at a static level one
     greater than that of the script containing the call to `eval`, because
     direct eval code runs within the caller's scope. However, a script for
     code passed to an indirect `eval` call is at static level zero, since it
     is evaluated in the global scope.
     Note that a generator's expressions are considered to be part of the
     body of a synthetic function, produced by the compiler.
     Scripts' static level be useful in deciding where to set breakpoints.
     For example, a breakpoint set on line 3 in this code:
         function f() {
           x = function g() {  // line 2
                               // line 3; no code here
             ...;
           }
         }
     should be set in `g`'s script, not in `f`'s, even though neither script
     contains code at that line. In such a case, the most deeply nested
     script—the one with the highest static level—should receive the
     breakpoint.
 `strictMode`
 :   This is `true` if this script's code is ECMAScript strict mode code, and
     `false` otherwise.
 `sourceMapURL`
 :   If this script was produced by a minimizer or translated from some other
     language, and we know the URL of a <b>source map</b> document relating
     the source positions in this script to the corresponding source
     positions in the original source, then this property's value is that
     URL. Otherwise, this is `null`.
     (On the web, the translator may provide the source map URL in a
     specially formatted comment in the JavaScript source code, or via a
     header in the HTTP reply that carried the generated JavaScript.)
 ## Function Properties of the Debugger.Script Prototype Object
 The functions described below may only be called with a `this` value
 referring to a `Debugger.Script` instance; they may not be used as
 methods of other kinds of objects.
 <code>decompile([<i>pretty</i>])</code>
 :   Return a string containing JavaScript source code equivalent to this
     script in its effect and result. If <i>pretty</i> is present and true,
     produce indented code with line breaks.
     (Note that [`Debugger.Object`][object] instances referring to functions also have
     a `decompile` method, whose result includes the function header and
     parameter names, so it is probably better to write
     <code><i>f</i>.decompile()</code> than to write
     <code><i>f</i>.getFunctionScript().decompile()</code>.)
 `getAllOffsets()`
 :   Return an array <i>L</i> describing the relationship between bytecode
     instruction offsets and source code positions in this script. <i>L</i>
     is sparse, and indexed by source line number. If a source line number
     <i>line</i> has no code, then <i>L</i> has no <i>line</i> property. If
     there is code for <i>line</i>, then <code><i>L</i>[<i>line</i>]</code> is an array
     of offsets of byte code instructions that are entry points to that line.
     For example, suppose we have a script for the following source code:
         a=[]
         for (i=1; i < 10; i++)
             // It's hip to be square.
             a[i] = i*i;
     Calling `getAllOffsets()` on that code might yield an array like this:
         [[0], [5, 20], , [10]]
     This array indicates that:
     * the first line's code starts at offset 0 in the script;
     * the `for` statement head has two entry points at offsets 5 and 20 (for
       the initialization, which is performed only once, and the loop test,
       which is performed at the start of each iteration);
     * the third line has no code;
     * and the fourth line begins at offset 10.
 <code>getLineOffsets(<i>line</i>)</code>
 :   Return an array of bytecode instruction offsets representing the entry
     points to source line <i>line</i>. If the script contains no executable
     code at that line, the array returned is empty.
 <code>getOffsetLine(<i>offset</i>)</code>
 :   Return the source code line responsible for the bytecode at
     <i>offset</i> in this script.
 `getChildScripts()`
 :   Return a new array whose elements are Debugger.Script objects for each
     function and each generator expression in this script. Only direct
     children are included; nested children can be reached by walking the
     tree.
 <code>setBreakpoint(<i>offset</i>, <i>handler</i>)</code>
 :   Set a breakpoint at the bytecode instruction at <i>offset</i> in this
     script, reporting hits to the `hit` method of <i>handler</i>. If
     <i>offset</i> is not a valid offset in this script, throw an error.
     When execution reaches the given instruction, SpiderMonkey calls the
     `hit<code> method of <i>handler</i>, passing a [</code>Debugger.Frame`][frame] instance
     representing the currently executing stack frame. The `hit` method's
     return value should be a [resumption value][rv], determining how execution should
     continue.
     Any number of breakpoints may be set at a single location; when control
     reaches that point, SpiderMonkey calls their handlers in an unspecified
     order.
     Any number of breakpoints may use the same <i>handler</i> object.
     Breakpoint handler method calls are cross-compartment, intra-thread
     calls: the call takes place in the same thread that hit the breakpoint,
     and in the compartment containing the handler function (typically the
     debugger's compartment).
     The new breakpoint belongs to the [`Debugger`][debugger-object] instance to which this
     script belongs; disabling the [`Debugger`][debugger-object] instance disables this
     breakpoint.
 <code>getBreakpoints([<i>offset</i>])</code>
 :   Return an array containing the handler objects for all the breakpoints
     set at <i>offset</i> in this script. If <i>offset</i> is omitted, return
     the handlers of all breakpoints set anywhere in this script. If
     <i>offset</i> is present, but not a valid offset in this script, throw
     an error.
 <code>clearBreakpoints(handler, [<i>offset</i>])</code>
 :   Remove all breakpoints set in this [`Debugger`][debugger-object] instance that use
     <i>handler</i> as their handler. If <i>offset</i> is given, remove only
     those breakpoints set at <i>offset</i> that use <i>handler</i>; if
     <i>offset</i> is not a valid offset in this script, throw an error.
     Note that, if breakpoints using other handler objects are set at the
     same location(s) as <i>handler</i>, they remain in place.
 <code>clearAllBreakpoints([<i>offset</i>])</code>
 :   Remove all breakpoints set in this script. If <i>offset</i> is present,
     remove all breakpoints set at that offset in this script; if
     <i>offset</i> is not a valid bytecode offset in this script, throw an
     error.

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js/src/doc/Debugger/Debugger.Script.md@6474c204b198 (annotated)

js/src/doc/Debugger/Debugger.Script.md