$observe() is a method on the Attributes object, and as such, it can only be used to observe/watch the value change of a DOM attribute.
($ observe（）是Attributes对象上的一种方法，因此，它只能用于观察/监视DOM属性的值更改。)
It is only used/called inside directives.(仅用于/调用内部指令。)
Use $observe when you need to observe/watch a DOM attribute that contains interpolation (ie, {{}}'s).(当需要观察/观察包含插值的DOM属性（即{{}}）时，请使用$ observe。)
Eg, attr1="Name: {{name}}" , then in a directive: attrs.$observe('attr1', ...) .(例如， attr1="Name: {{name}}" ，然后在指令中： attrs.$observe('attr1', ...) 。)
(If you try scope.$watch(attrs.attr1, ...) it won't work because of the {{}}s -- you'll get undefined .) Use $watch for everything else.(（如果尝试使用scope.$watch(attrs.attr1, ...) ，则由于{{}}而无法正常工作-您将无法undefined 。）将$ watch用于其他所有内容。)
$watch() is more complicated.
($ watch（）更复杂。)
It can observe/watch an "expression", where the expression can be either a function or a string.(它可以观察/观察“表达式”，其中表达式可以是函数或字符串。)
If the expression is a string, it is $parse 'd (ie, evaluated as an Angular expression ) into a function.(如果表达式是字符串，则将$ parse'd （即，作为Angular表达式求值）放入函数中。)
(It is this function that is called every digest cycle.) The string expression can not contain {{}}'s.(（每个摘要周期都会调用此函数。）字符串表达式不能包含{{}}。)
$watch is a method on the Scope object, so it can be used/called wherever you have access to a scope object, hence in($ watch是Scope对象上的一种方法，因此可以在任何有权访问scope对象的地方使用/调用它，因此在)
Because strings are evaluated as Angular expressions, $watch is often used when you want to observe/watch a model/scope property.
(因为字符串是作为Angular表达式求值的，所以当您要观察/观察模型/作用域属性时，通常使用$ watch。)
Eg, attr1="myModel.some_prop" , then in a controller or link function: scope.$watch('myModel.some_prop', ...) or scope.$watch(attrs.attr1, ...) (or scope.$watch(attrs['attr1'], ...) ).(例如， attr1="myModel.some_prop" ，然后在控制器或链接函数中： scope.$watch('myModel.some_prop', ...)或scope.$watch(attrs.attr1, ...) （或scope.$watch(attrs['attr1'], ...) ）。)
(If you try attrs.$observe('attr1') you'll get the string myModel.some_prop , which is probably not what you want.)(（如果尝试使用attrs.$observe('attr1') ， myModel.some_prop获得字符串myModel.some_prop ，这可能不是您想要的。）)
As discussed in comments on @PrimosK's answer, all $observes and $watches are checked every digest cycle .
(如对@PrimosK答案的评论中所讨论的，每个摘要周期都会检查所有$ observes和$ watches。)
Directives with isolate scopes are more complicated.
(具有单独作用域的指令更加复杂。)
If the '@' syntax is used, you can $observe or $watch a DOM attribute that contains interpolation (ie, {{}}'s).(如果使用“ @”语法，则可以$ observ 或$ watch包含插值（即{{}}）的DOM属性。)
(The reason it works with $watch is because the '@' syntax does the interpolation for us, hence $watch sees a string without {{}}'s.) To make it easier to remember which to use when, I suggest using $observe for this case also.(（它与$ watch一起使用的原因是因为'@'语法为我们进行了插值 ，因此$ watch看到的字符串中没有{{}}。）为了更容易记住何时使用哪个字符串，我建议使用$在这种情况下也要观察。)
To help test all of this, I wrote a Plunker that defines two directives.
(为了帮助测试所有这些，我编写了一个Plunker ，它定义了两个指令。)
One ( d1 ) does not create a new scope, the other ( d2 ) creates an isolate scope.(一个（ d1 ）不创建新的作用域，另一个（ d2 ）创建隔离的作用域。)
Each directive has the same six attributes.(每个指令具有相同的六个属性。)
Each attribute is both $observe'd and $watch'ed.(每个属性都是$ observe'd和$ watch'ed。)
<div d1 attr1="{{prop1}}-test" attr2="prop2" attr3="33" attr4="'a_string'"
attr5="a_string" attr6="{{1+aNumber}}"></div>
Look at the console log to see the differences between $observe and $watch in the linking function.
(查看控制台日志，以查看链接功能中$ observe和$ watch之间的区别。)
Then click the link and see which $observes and $watches are triggered by the property changes made by the click handler.(然后单击链接，查看单击处理程序所做的属性更改触发了哪些$ observes和$ watches。)
Notice that when the link function runs, any attributes that contain {{}}'s are not evaluated yet (so if you try to examine the attributes, you'll get undefined ).
(请注意，当链接函数运行时，尚未评估任何包含{{}}的属性（因此，如果您尝试检查这些属性，则会得到undefined ）。)
The only way to see the interpolated values is to use $observe (or $watch if using an isolate scope with '@').(查看插值的唯一方法是使用$ observe（如果使用带'@'的隔离范围，则使用$ watch）。)
Therefore, getting the values of these attributes is an asynchronous operation.(因此，获取这些属性的值是异步操作。)
(And this is why we need the $observe and $watch functions.)(（这就是为什么我们需要$ observe和$ watch函数。）)
Sometimes you don't need $observe or $watch.
(有时您不需要$ observe或$ watch。)
Eg, if your attribute contains a number or a boolean (not a string), just evaluate it once: attr1="22" , then in, say, your linking function: var count = scope.$eval(attrs.attr1) .(例如，如果您的属性包含数字或布尔值（不是字符串），则只需对其进行一次评估： attr1="22" ，然后在例如您的链接函数中： var count = scope.$eval(attrs.attr1) 。)
If it is just a constant string – attr1="my string" – then just use attrs.attr1 in your directive (no need for $eval()).(如果它只是一个常量字符串– attr1="my string" –则只需在指令中使用attrs.attr1 （不需要$ eval（））。)
See also Vojta's google group post about $watch expressions.
(另请参见Vojta在Google网上论坛上发布的有关$ watch表达式的信息。)
