blocks|key|1309693|text|这就是肮脏检查的工作原理。每当$scope上的某物发生变化时，角度就会通过附加到范围的所有东西来旋转，并且它会一直这样做，直到没有更多的变化。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1309694|如果您想这样做，您必须确保您的$watch函数是幂等的。您必须同时查看newValue和oldValue，并确定您是否已经在这个$digest循环中将这些更改应用于您的变量。如何做到这一点在一定程度上取决于您对someVar所做的更改。|1309695|一般来说，在手表函数中改变一个观察变量并不是一个好主意.|1309696|entityMap^0|F|6|0|F|6|Z|8|18|8|1S|7|2X|7|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|Z|8|@]|D|@]|E|$]]|$1|J|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|K|$]]

This is how dirty-checking works. Every time something on the <code>$scope</code> changes Angular will spin through everything that is attached to the scope and it will keep doing so untill there are no more changes.

If you want to do something like that, you will have to make sure that your <code>$watch</code> function is idempotent. You will have to look at both <code>newValue</code> and <code>oldValue</code> and figure out wether you've already applied the changes to your variable in this <code>$digest</code> loop. How you can do that depends a bit on what kind of changes you're doing to <code>someVar</code>.

Generally speaking, changing a watched variable in a watch-function is unfortunately not a good idea.

blocks|key|70461|text|是的，你可以这样取消|type|unstyled|depth|inlineStyleRanges|entityRanges|data|70462|var+wathcer+=+scope.$watch('someVar',+function(newValue,+oldValue)+{
++++console.log(newValue);
++++scope.someVar+=+[Do+something+with+someVar];

});
wathcer();+//+clear+the+watch|code-block|syntax|javascript|70463|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

yes you can cancel it like this 

<pre><code>var wathcer = scope.$watch('someVar', function(newValue, oldValue) {
 console.log(newValue);
 scope.someVar = [Do something with someVar];

});
wathcer(); // clear the watch
</code></pre>

blocks|key|492643|text|函数内部使用如果条件可以避免连续的循环|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|492644|scope.$watch('someVar',+function(newValue,+oldValue)+{
+++if(newValue!==oldValue)+{
++++console.log(newValue);
++++scope.someVar+=+[Do+something+with+someVar];
+++}+
});|code-block|syntax|javascript|492645|entityMap^0|6|2|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Inside function use if condition to avoide continues for loop 

<pre><code>scope.$watch('someVar', function(newValue, oldValue) {
 if(newValue!==oldValue) {
 console.log(newValue);
 scope.someVar = [Do something with someVar];
 } 
});
</code></pre>

blocks|key|70525|text|您可以使用bool变量管理它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|70526|$scope.someVarChanged+=+false;

scope.$watch('someVar',+function(newValue,+oldValue)+{
++++console.log(newValue);
++++$scope.someVarChanged+=+!$scope.someVarChanged!;
++++if($scope.someVarChanged)+{++++++++++++
++++++++scope.someVar+=+[Do+something+with+someVar];
++++}
});|code-block|syntax|javascript|70527|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

you can manage it using a bool variable

<pre><code>$scope.someVarChanged = false;

scope.$watch('someVar', function(newValue, oldValue) {
 console.log(newValue);
 $scope.someVarChanged = !$scope.someVarChanged!;
 if($scope.someVarChanged) { 
 scope.someVar = [Do something with someVar];
 }
});
</code></pre>

blocks|key|492664|text|当使用$scope.$watch监视变量的变化时，角度检查引用是否已更改。如果有，则执行$watch处理程序来更新视图。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|492665|如果计划在$watch处理程序中更改范围变量，它将触发无限$digest循环，因为范围变量引用每次调用时都会更改。|492666|绕过无限摘要问题的诀窍是使用(文档)保存$watch处理程序中的引用：|BOLD|492667|scope.$watch('someVar',+function(newValue,+oldValue)+{
++++console.log(newValue);
++++var+someVar+=+[Do+something+with+someVar];

++++//+angular+copy+will+preserve+the+reference+of+$scope.someVar
++++//+so+it+will+not+trigger+another+digest+
++++angular.copy(someVar,+$scope.someVar);

});|code-block|syntax|javascript|492668|注意:此技巧仅适用于对象引用。它将不适用于原语。|492669|通常，在自己的$watched侦听器中更新$watch变量不是一个好主意。然而，有时这可能是不可避免的。|492670|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.angularjs.org/api/ng/function/angular.copy^0|3|D|18|6|0|0|E|L|K|6|F|2|0|0|0|0|O|0|0|1G|7|8|L|6|0^^$0|@$1|2|3|4|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|16|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|17|8|@$9|18|A|19|B|J]|$9|1A|A|1B|B|C]]|D|@$9|1C|A|1D|1|1E]]|E|$]]|$1|K|3|L|5|M|7|1F|8|@]|D|@]|E|$N|O]]|$1|P|3|Q|5|6|7|1G|8|@$9|1H|A|1I|B|J]]|D|@]|E|$]]|$1|R|3|S|5|6|7|1J|8|@$9|1K|A|1L|B|J]|$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1Q|8|@]|D|@]|E|$]]]|U|$V|$5|W|X|Y|E|$Z|10]]]]

When a variable is watched for changes using <code>$scope.$watch</code>, angular checks if the reference has changed. If it has, then the <code>$watch</code> handler is executed to update the view. 

If you plan on changing the scope variable within the $watch handler, it will trigger an infinite $digest loop because the scope variable reference changes every time that it is called. 

The trick to getting around the infinite digest issue is to preserve the reference inside your <code>$watch</code> handler using angular.copy (<a href="https://docs.angularjs.org/api/ng/function/angular.copy" rel="noreferrer">docs</a>):

<pre><code>scope.$watch('someVar', function(newValue, oldValue) {
 console.log(newValue);
 var someVar = [Do something with someVar];

 // angular copy will preserve the reference of $scope.someVar
 // so it will not trigger another digest 
 angular.copy(someVar, $scope.someVar);

});
</code></pre>

Note: This trick only works for object references. It will not work with primitives.

In general, its not a good idea to update a <code>$watched</code> variable within its own <code>$watch</code> listener. However, sometimes it may be unavoidable.

In AngularJS I have a directive that watches a scope variable. When the variable contains certain data then I need to alter that variable a bit. The problem is that when I change the variable that my <code>$watch</code> is triggered again. So I end up in a continuous loop.

<pre><code>scope.$watch('someVar', function(newValue, oldValue) {
 console.log(newValue);
 scope.someVar = [Do something with someVar];
});
</code></pre>

This keeps triggering <code>$watch</code> again, which makes sense. But I do need a way to change the watched variable. Is there a way to do this?

Watch variable and change it

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在AngularJS中，我有一个监视作用域变量的指令。当变量包含某些数据时，我需要稍微修改该变量。问题是，当我更改变量时，我的$watch再次被触发。所以我最终成了一个连续的循环。scope.$watch('someVar', function(newValue, oldValue) {    console.log(...

问观察变量并更改它
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