angular.js/docs/content/error/compile/nonassign.ngdoc

@ngdoc error
@name $compile:nonassign
@fullName Non-Assignable Expression
@description

This error occurs when a directive defines an isolate scope property that support two-way data-binding (using the `=` mode in the {@link guide/directive#directivedefinitionobject  directive definition}) but the directive is used with an expression that is not-assignable.

In order for the two-way data-binding to work, it must be possible to write new values back into the path defined with the expression.

For example, given a directive:

```
myModule.directive('myDirective', function factory() {
  return {
    ...
    scope: {
      'bind': '=localValue'
    }
    ...
  }
});
```

Following are invalid uses of this directive:
```
<!-- ERROR because `1+2=localValue` is an invalid statement -->
<my-directive bind="1+2">

<!-- ERROR because `myFn()=localValue` is an invalid statement -->
<my-directive bind="myFn()">
```


To resolve this error, always use path expressions with scope properties that are two-way data-bound:
```
<my-directive bind="some.property">
<my-directive bind="some[3]['property']">
```