ngModel Formatters and Parsers

Question

I posted the same question in different form, but no one answered. I am not getting a clear picture of what the Formatters and Parsers do in angular js.

By the definition, both the Formatters and Parsers look similar to me. Maybe I am wrong, as I am new to this angularjs.

Formatters Definition

Array of functions to execute, as a pipeline, whenever the model value changes. Each function is called, in turn, passing the value through to the next. Used to format / convert values for display in the control and validation.

Parsers Definition

Array of functions to execute, as a pipeline, whenever the control reads value from the DOM. Each function is called, in turn, passing the value through to the next. Used to sanitize / convert the value as well as validation. For validation, the parsers should update the validity state using $setValidity(), and return undefined for invalid values.

Please help me to understand both features with a simple example. A simple illustration of both will be appreciated.

Answer 1

This topic was covered really well in a related question: How to do two-way filtering in AngularJS?

To summarize:

• Formatters change how model values will appear in the view.
• Parsers change how view values will be saved in the model.

Here is a simple example, building on an example in the NgModelController api documentation:

  //format text going to user (model to view)
  ngModel.$formatters.push(function(value) {
    return value.toUpperCase();
  });

  //format text from the user (view to model)
  ngModel.$parsers.push(function(value) {
    return value.toLowerCase();
  });

You can see it in action: http://plnkr.co/UQ5q5FxyBzIeEjRYYVGX?plnkr=legacy

<input type="button" value="set to 'misko'" ng-click="data.name='misko'"/>
<input type="button" value="set to 'MISKO'" ng-click="data.name='MISKO'"/>
<input changecase ng-model="data.name" />

When you type a name in (view to model), you will see that the model is always lowercase. But, when you click a button and programatically change the name (model to view), the input field is always uppercase.