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| __NOTOC__
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| {{Greasemonkey Manual TOC}}
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| == Why a Special Environment? == | | == I am shz == |
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| When [[Greasemonkey]] executes a [[user script]] it does so in a special [[sandbox]] environment.
| | == 相册 == |
| [[Greasemonkey]] takes advantage of a Firefox feature called [[XPCNativeWrappers]] to insulate the [[user script]] from the content web page, which it references. | | [/media/本地磁盘/照片/李嫣然] |
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| Although this makes it more difficult, or impossible, to do certain things in a script, it is a necessary evil.
| | == end == |
| Earlier [[version history|versions]] of [[Greasemonkey]] had no such sandbox, and as a result, [[security]] holes were uncovered.
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| [[Greasemonkey]] provides certain enhanced [[Greasemonkey Manual:APIs|APIs]] to the [[user script]], so that it may accomplish things that a regular web page's JavaScript cannot.
| | == welcome == |
| This useful feature has enabled some of the most popular scripts.
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| Unfortunately, when abused, these powerful features can create serious problems.
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| No exploits were ever uncovered in the wild, but the potential was too great, so the sandbox environment was created.
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| Luckily, for almost all the difficulties that the sandbox environment provides, there are ways to still accomplish the desired goal.
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| The article [[Avoid Common Pitfalls in Greasemonkey]] does a wonderful job explaining what the most common snags are, and for each one explains the way to work around the problem.
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| It is essential reading for any script author.
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| Finally, of note is the [[unsafeWindow]] object present in the sandbox.
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| As the name implies, use of this object is ''unsafe''!
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| This is the raw, un-sandboxed "window" of the content page.
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| Certain limited tasks can only be accomplished by referencing this raw window directly, but be warned!
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| JavaScript is a complicated and intricate language, even the most basic operations can be redefined by the content page to perform other actions.
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| The sandbox environment is provided for the safety of any user of a script.
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| If at all possible, use of [[unsafeWindow]] should be avoided.
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| == What's Missing? == | |
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| Depending on the usage, the special [[Greasemonkey]] environment may seem perfectly normal, or excessively limiting.
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| The Greasemonkey environment is a vanilla [[XPCNativeWrapper]] of the content window, with only certain extra bits added in to emulate a normal environment, or changed. Specifically:
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| :* <code>window</code> is an [[XPCNativeWrapper|XPCNativeWrapper]] of the content window.
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| :* <code>document</code> is the document object of the XPCNativeWrapper window object.
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| :* [[XPathResult]] is added so that <code>document.evaluate()</code> works.
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| :* Unless the [[Metadata Block#.40unwrap|@unwrap]] metadata imperative is present in the user script header, the entire script is wrapped inside an [http://en.wikipedia.org/wiki/Anonymous_function anonymous function], to guarantee the script's identifiers do not collide with identifiers present in the Mozilla JavaScript sandbox. This function wrapper captures any function definitions and <code>var</code> variable declarations made (e.g. <code>var i = 5;</code>) into the function's local scope. Declarations made without <code>var</code> will however end up on the script's <code>this</code> object, which in Greasemonkey is the global object, contrary to in the normal browser object model, where the <code>window</code> object fills this function. In effect, after <code>i = 5;</code>, the values of <code>window['i']</code> and <code>window.i</code> remain undefined, whereas <code>this['i']</code> and <code>this.i</code> will be 5. See also: [[Global_object]]
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| :* In order to access variables on the page, use the [[unsafeWindow]] object. To use values defined in a script, simply reference them by their names.
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| Since Mozilla provides a rich environment, there are a wide variety of things that have ''not'' been imported from the general content scope into the Greasemonkey sandbox.
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| Including, but not limited to:
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| :* [https://developer.mozilla.org/en/DOM/document.createTreeWalker document.createTreeWalker]
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| :* [http://www.xulplanet.com/references/objref/SOAPCall.html SOAPCall]
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| The more esoteric the method, the ''less likely'' that it has been included in the Greasemonkey sandbox.
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| == See also ==
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| * Wikipedia: [http://en.wikipedia.org/wiki/Sandbox_(computer_security) Sandbox]
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| * [[Security]]
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| * [http://www.oreillynet.com/pub/a/network/2005/11/01/avoid-common-greasemonkey-pitfalls.html Avoid Common Pitfalls in Greasemonkey]
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