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