Angular中的$watch、$watchGroup、$watchCollection

• 1,原型:$watch: function(watchExp, listener, objectEquality, prettyPrintExpression){}; • 2,参数:watchExp(必须):{(function()|string)},可以字符串表达式,也可以带当前scope为参数的函数 • - `string`: Evaluated as {@link guide/expression expression} • - `function(scope)`: called with current `scope` as a parameter. • 3