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Debugger: Difference between revisions
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→Debug.Frame: formatting; clarifications.
(→Debug.Frame: First cut.) |
m (→Debug.Frame: formatting; clarifications.) |
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==Debug.Frame== | ==Debug.Frame== | ||
A <code>Debug.Frame</code> instance represents a debuggee stack frame. | A <code>Debug.Frame</code> instance represents a debuggee stack frame. Given a <code>Debug.Frame</code> instance, you can find the script the frame is executing, walk the stack to older frames, find the lexical environment in which the execution is taking place, and so on. | ||
SpiderMonkey creates instances of <code>Debug.Frame</code> as needed in two situations: when it calls a hook function that expects a frame as an argument, and when the debugger reads an existing frame's <code>older</code> property. SpiderMonkey creates only one <code>Debug.Frame</code> instance for a given debuggee frame; every hook function called while the debuggee is running in a given frame receives the same frame object; and walking the stack back to a previously accessed frame yields the same frame object as before. Debugger code can add its own properties to a frame object and expect to find them later, use <code>==</code> to decide whether two expressions refer to the same frame, and so on. | |||
A <code>Debug.Frame</code> instance is a weak reference to the frame; once the debuggee destroys the frame (perhaps by returning from the function or completing the <code>eval</code> call), the <code>Debug.Frame</code> instance becomes inactive: its properties become undefined, and calls to its methods will throw an exception. | |||
A <code>Debug.Frame</code> instance has the following properties, which are all non-writable and non-configurable: | A <code>Debug.Frame</code> instance has the following properties, which are all non-writable and non-configurable: | ||
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<dd>A string describing what sort of frame this is: | <dd>A string describing what sort of frame this is: | ||
<ul> | <ul> | ||
<li><code>"call"</code>: a frame running a function | <li><code>"call"</code>: a frame running a function call. | ||
<li><code>"eval"</code>: a frame running code passed to <code>eval</code>. | <li><code>"eval"</code>: a frame running code passed to <code>eval</code>. | ||
<li><code>"global"</code>: a frame running global code (JavaScript that is neither of the above) | <li><code>"global"</code>: a frame running global code (JavaScript that is neither of the above) | ||
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<li><code>"dummy"</code>: a frame pushed for stupid people (rather—I don't know what this is) | <li><code>"dummy"</code>: a frame pushed for stupid people (rather—I don't know what this is) | ||
</ul> | </ul> | ||
(Note that a <code>"debugger"</code> frame represents the debugger continuation expecting the expression's value; the expression itself has its own <code>"eval"</code> frame.) | (Note that a <code>"debugger"</code> frame represents the debugger continuation expecting the expression's value; the expression itself has its own <code>"eval"</code> frame.) | ||
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<dt>eval(<i>code</i>) | <dt>eval(<i>code</i>) | ||
<dd>Begin evaluating <i>code</i> in the scope of this frame. <i>Code</i> is a string. This pushes a <code>"debugger"</code> frame on the debuggee's stack, evaluates <i>code</i> with all extant hook functions active, and returns a value of the sort passed to an <code>enterFrame</code> completion function describing how the code completed. | <dd>Begin evaluating <i>code</i> in the scope of this frame. <i>Code</i> is a string. This pushes a <code>"debugger"</code> frame on the debuggee's stack, evaluates <i>code</i> with all extant hook functions active, and returns a value of the sort passed to an <code>enterFrame</code> completion function describing how the code completed. | ||
Note that, although this method mixes the debugger's own stack frames with the debuggee's, walking the stack only shows the debuggee's frames; the continuation of the debugger's call to this method, up to the debugging hook function call, is represented by a single <code>"debugger"</code> frame. | |||
<dt>finish(<i>result</i>) <i>(future plan)</i> | <dt>finish(<i>result</i>) <i>(future plan)</i> | ||