使用 Chrome 扩展程序停止执行函数 [英] Stop a function from execute with Chrome extension
问题描述
这是一个简单的页面:
<!DOCTYPE HTML>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Test page</title>
<script type="text/javascript">
function foo (num) {
alert(num);
}
</script>
</head>
<body>
Hello World
<script type="text/javascript">
foo(2);
</script>
</body>
</html>
我想编写一个 Chrome 扩展程序来防止执行底层脚本 (foo(2)).
我试图编写一个内容脚本，它删除了最后一个脚本标签:
I'd like to write a Chrome extension to prevent the execute of the bottom script(foo(2)).
I tried to write a content script which removes the last script tag with:
document.body.removeChild(document.body.lastChild);
但它不起作用.
我认为这可能是因为内容脚本在最后一个脚本行执行后运行.然后我尝试将 run_at 设置为 document_start 或 document_end，但它们都不适合我..
I think this may be because the content script runs after the last script line has executed. then I tried to set the run_at to document_start or document_end, but none of them work for me..
推荐答案
我在开发 不要跟踪我 Google 用户脚本/扩展.
I faced the same problem during development of the Don't track me Google User script / extension.
#重要提示Chrome 内容脚本中的 window 对象无法以任何方式直接访问.
我测试了很多方法，唯一可靠的方法是通过动态创建的脚本标记注入代码.看看这个答案，或我的扩展程序的源代码 了解更多信息.
#Important note The
windowobject in a Chrome contentscript cannot be accessed directly, in any way.
I have tested many methods, and the only reliable method is injecting the code through a dynamically created script tag. Have a look at this answer, or my extension's source code for more information.
我使用 Object.defineProperty.使用此方法，您可以定义一个属性，并指定有关 getter、setter 和属性描述符的信息.在你的情况下:
I solved it by using Object.defineProperty. With this method, you can define a property, and specify information about the getter, setter and property descriptors. In your case:
Object.defineProperty(window, 'foo', {
value: function(){/*This function cannot be overridden*/}
});
或者，如果您想捕获该变量，并在以后使用它:
Or, if you want to capture the variable, and use it later:
(function() {
var originalFoo = function(){/*Default*/};
Object.defineProperty(window, 'foo', {
get: function(){
if (confirm('function logic')) return function(){/*dummy*/};
else return originalFoo;
},
set: function(fn){originalFoo = fn;}
});
})();
##Bug 在 Chrome 17
见 http://jsfiddle.net/bHUag/
请注意，当函数声明和属性描述符方法位于同一块中时，此错误 *似乎* 不适用.不过，这是错误的.效果是不可见的，因为函数声明总是在代码块之前进行评估.因此，首先评估 `function foo(){}`，然后是其余的代码.
##Bug in Chrome 17
See http://jsfiddle.net/bHUag/
Note that this bug *seems* to not be applied when the function declaration and property descriptor method are in the same block. This is false, though. The effect is not visible, because function declarations are always evaluated before the code block. So, `function foo(){}` is evaluated first, then the rest of the code.
<script>
Object.defineProperty(window, 'foo', {value: function(){return 5;} });
</script><script>
function foo(){return 1};
alert(foo()); // Shows 5 in all browsers except for Chrome v17
</script>
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