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

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

js/src/doc/Debugger/Debugger.Environment.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.Environment
 A `Debugger.Environment` instance represents a lexical environment,
 associating names with variables. Each [`Debugger.Frame`][frame] instance
 representing a debuggee frame has an associated environment object
 describing the variables in scope in that frame; and each
 [`Debugger.Object`][object] instance representing a debuggee function has an
 environment object representing the environment the function has closed
 over.
 ECMAScript environments form a tree, in which each local environment is
 parented by its enclosing environment (in ECMAScript terms, its 'outer'
 environment). We say an environment <i>binds</i> an identifier if that
 environment itself associates the identifier with a variable, independently
 of its outer environments. We say an identifier is <i>in scope</i> in an
 environment if the identifier is bound in that environment or any enclosing
 environment.
 SpiderMonkey creates `Debugger.Environment` instances as needed as the
 debugger inspects stack frames and function objects; calling
 `Debugger.Environment` as a function or constructor raises a `TypeError`
 exception.
 SpiderMonkey creates exactly one `Debugger.Environment` instance for each
 environment it presents via a given [`Debugger`][debugger-object] instance:
 if the debugger encounters the same environment through two different
 routes (perhaps two functions have closed over the same environment),
 SpiderMonkey presents the same `Debugger.Environment` instance to the
 debugger each time. This means that the debugger can use the `==` operator
 to recognize when two `Debugger.Environment` instances refer to the same
 environment in the debuggee, and place its own properties on a
 `Debugger.Environment` instance to store metadata about particular
 environments.
 (If more than one [`Debugger`][debugger-object] instance is debugging the
 same code, each [`Debugger`][debugger-object] gets a separate
 `Debugger.Environment` instance for a given environment. This allows the
 code using each [`Debugger`][debugger-object] instance to place whatever
 properties it likes on its own [`Debugger.Object`][object] instances,
 without worrying about interfering with other debuggers.)
 If a `Debugger.Environment` instance's referent is not a debuggee
 environment, then attempting to access its properties (other than
 `inspectable`) or call any its methods throws an instance of `Error`.
 `Debugger.Environment` instances protect their referents from the
 garbage collector; as long as the `Debugger.Environment` instance is
 live, the referent remains live. Garbage collection has no visible
 effect on `Debugger.Environment` instances.
 ## Accessor Properties of the Debugger.Environment Prototype Object
 A `Debugger.Environment` instance inherits the following accessor
 properties from its prototype:
 `inspectable`
 :   True if this environment is a debuggee environment, and can therefore
     be inspected. False otherwise. All other properties and methods of
     `Debugger.Environment` instances throw if applied to a non-inspectable
     environment.
 `type`
 :   The type of this environment object, one of the following values:
     * "declarative", indicating that the environment is a declarative
       environment record. Function calls, calls to `eval`, `let` blocks,
       `catch` blocks, and the like create declarative environment records.
     * "object", indicating that the environment's bindings are the
       properties of an object. The global object and DOM elements appear in
       the chain of environments via object environments. (Note that `with`
       statements have their own environment type.)
     * "with", indicating that the environment was introduced by a `with`
       statement.
 `parent`
 :   The environment that encloses this one (the "outer" environment, in
     ECMAScript terminology), or `null` if this is the outermost environment.
 `object`
 :   A [`Debugger.Object`][object] instance referring to the object whose
     properties this environment reflects. If this is a declarative
     environment record, this accessor throws a `TypeError` (since
     declarative environment records have no such object). Both `"object"`
     and `"with"` environments have `object` properties that provide the
     object whose properties they reflect as variable bindings.
 `callee`
 :   If this environment represents the variable environment (the top-level
     environment within the function, which receives `var` definitions) for
     a call to a function <i>f</i>, then this property's value is a
     [`Debugger.Object`][object] instance referring to <i>f</i>. Otherwise,
     this property's value is `null`.
 ## Function Properties of the Debugger.Environment Prototype Object
 The methods described below may only be called with a `this` value
 referring to a `Debugger.Environment` instance; they may not be used as
 methods of other kinds of objects.
 `names()`
 :   Return an array of strings giving the names of the identifiers bound by
     this environment. The result does not include the names of identifiers
     bound by enclosing environments.
 <code>getVariable(<i>name</i>)</code>
 :   Return the value of the variable bound to <i>name</i> in this
     environment, or `undefined` if this environment does not bind
     <i>name</i>. <i>Name</i> must be a string that is a valid ECMAScript
     identifier name. The result is a debuggee value.
     JavaScript engines often omit variables from environments, to save space
     and reduce execution time. If the given variable should be in scope, but
     `getVariable` is unable to produce its value, it returns an ordinary
     JavaScript object (not a [`Debugger.Object`][object] instance) whose
     `optimizedOut` property is `true`.
     This is not an [invocation function][inv fr];
     if this call would cause debuggee code to run (say, because the
     environment is a `"with"` environment, and <i>name</i> refers to an
     accessor property of the `with` statement's operand), this call throws a
     [`Debugger.DebuggeeWouldRun`][wouldrun]
     exception.
 <code>setVariable(<i>name</i>, <i>value</i>)</code>
 :   Store <i>value</i> as the value of the variable bound to <i>name</i> in
     this environment. <i>Name</i> must be a string that is a valid
     ECMAScript identifier name; <i>value</i> must be a debuggee value.
     If this environment binds no variable named <i>name</i>, throw a
     `ReferenceError`.
     This is not an [invocation function][inv fr];
     if this call would cause debuggee code to run, this call throws a
     [`Debugger.DebuggeeWouldRun`][wouldrun]
     exception.
 <code>getVariableDescriptor(<i>name</i>)</code>
 :   Return an property descriptor describing the variable bound to
     <i>name</i> in this environment, of the sort returned by
     `Debugger.Object.prototype.getOwnPropertyDescriptor`. <i>Name</i> must
     be a string whose value is a valid ECMAScript identifier name.
     If this is an `"object"` or `"with"` environment record, this simply
     returns the descriptor for the given property of the environment's
     object. If this is a declarative environment record, this returns a
     descriptor reflecting the binding's mutability as the descriptor's
     `writable` property, and its deletability as the descriptor's
     `configurable` property. All declarative environment record bindings are
     marked as `enumerable`. <i>(This isn't great; the semantics of variables
     in declarative enviroments don't really match those of properties, so
     writing code that operates properly on descriptors for either kind may
     be difficult.)</i>
     If this environment binds no variable named <i>name</i>, throw a
     `ReferenceError`.
 <code>defineVariable(<i>name</i>, <i>descriptor</i>)</code>
 :   Create or reconfigure the variable bound to <i>name</i> in this
     environment according to <i>descriptor</i>. <i>Descriptor</i> is the
     sort of value returned by `getVariableDescriptor`. On success, return
     `undefined`; on failure, throw an appropriate exception. <i>Name</i>
     must be a string whose value is a valid ECMAScript identifier name.
     If implementation restrictions prevent SpiderMonkey from creating or
     reconfiguring the variable as requested, this call throws an `Error`
     exception.
 <code>deleteVariable(<i>name</i>)</code>
 :   Delete this environment's binding for <i>name</i>.
     If this environment binds no variable named <i>name</i>, throw a
     `ReferenceError`.
     If implementation restrictions prevent SpiderMonkey from deleting the
     variable as requested, this call throws an `Error` exception.
 <code>find(<i>name</i>)</code>
 :   Return a reference to the innermost environment, starting with this
     environment, that binds <i>name</i>. If <i>name</i> is not in scope in
     this environment, return `null`. <i>Name</i> must be a string whose
     value is a valid ECMAScript identifier name.
 <code>eval(<i>code</i>)</code> <i>(future plan)</i>
 :   Evaluate <i>code</i> in this environment, and return a
     [completion value][cv] describing how it completed. <i>Code</i> is a
     string. All extant handler methods, breakpoints, watchpoints, and so on
     remain active during the call. This function follows the
     [invocation function conventions][inv fr].
     <i>Code</i> is interpreted as strict mode code when it contains a Use
     Strict Directive.
     If <i>code</i> is not strict mode code, then variable declarations in
     <i>code</i> affect this environment. (In the terms used by the
     ECMAScript specification, the `VariableEnvironment` of the execution
     context for the eval code is the `VariableEnvironment` this
     `Debugger.Environment` instance represents.) If implementation
     restrictions prevent SpiderMonkey from extending this environment as
     requested, this call throws an `Error` exception.
 <code>evalWithBindings(<i>code</i>, <i>bindings</i>)</code> <i>(future plan)</i>
 :   Like `eval`, but evaluate <i>code</i> in this environment, extended with
     bindings from the object <i>bindings</i>. For each own enumerable
     property of <i>bindings</i> named <i>name</i> whose value is
     <i>value</i>, include a variable in the environment in which <i>code</i>
     is evaluated named <i>name</i>, whose value is <i>value</i>. Each
     <i>value</i> must be a debuggee value. (This is not like a `with`
     statement: <i>code</i> may access, assign to, and delete the introduced
     bindings without having any effect on the <i>bindings</i> object.)
     This method allows debugger code to introduce temporary bindings that
     are visible to the given debuggee code and which refer to debugger-held
     debuggee values, and do so without mutating any existing debuggee
     environment.
     Note that, like `eval`, declarations in the <i>code</i> passed to
     `evalWithBindings` affect this environment, even as <i>code</i> is
     evaluated with <i>bindings</i> visible. (In the terms used by the
     ECMAScript specification, the `VariableEnvironment` of the execution
     context for the eval code is the `VariableEnvironment` this environment
     represents, and the <i>bindings</i> appear in a new declarative
     environment, which is the eval code's `LexicalEnvironment`.) If
     implementation restrictions prevent SpiderMonkey from extending this
     environment as requested, this call throws an `Error` exception.

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

js/src/doc/Debugger/Debugger.Environment.md