It’s possible to implement your own field validation function in Alfresco Share in JS by overwriting Share mandatory constraint which uses
Alfresco.forms.validation.mandatory located in /opt/alfresco-3.4.d/tomcat/webapps/share/js/forms-runtime.js
The default configuration can be suppressed the way described here:http://wiki.alfresco.com/wiki/Forms#constraint-handlers
validation-handler parameter is the name of your own JS function.
Here you can find description of validation function parameters http://wiki.alfresco.com/wiki/Forms_Developer_Guide#Validation_Handlers

In the current version of Alfresco (3.4d) the validation ‘fails silently’ which means you can’t dynamically display error message. When validation fails it’s not possible to submit the form. There are foundations for enhancement of this mechanism so it’s quite possible the ‘full’ validation will be available in near future.
You can

download full eclipse ant project for my example here

. I will provide
instructions for manual installation as well.
Ant installation
1. Set paths to tomcat directory in build.properties
TOMCAT_HOME=/opt/alfresco-3.4.d/tomcatAPP_TOMCAT_HOME=/opt/alfresco-3.4.d/tomcat
2. Just run ‘ant’ in project directory.

So, let’s start the core of this tutorial.
1. I implemented my own simple data model for this example. As it is not complicated, nor directly connected with validation its self I just attach needed files with my project.If you’re not familiar with defining data models you can read about it for instance, here
tutorial:http://www.tribloom.com/blogs/michael/2011/04/18/alfresco-repository-webscript/

detailed documentation: http://wiki.alfresco.com/wiki/Data_Dictionary_Guide#The_Data_Dictionary
validationModel.xml goes to /opt/alfresco-3.4.d/tomcat/webapps/alfresco/WEB-INF/classes/alfresco/extension/model
validation-model-context.xml goes to /opt/alfresco-3.4.d/tomcat/webapps/alfresco/WEB-INF/classes/alfresco/extension/

2. share-config-validation-custom.xml goes to /opt/alfresco-3.4.d/tomcat/webapps/share/WEB-INF/classes/alfresco/web-extension
This file contains definition of create and edit forms for the new data type.
Piece of code concerning validation:

<field id="ex:gross" label-id="example.price.gross" mandatory="true"
	help-id="example.price.gross.help">
	<constraint-handlers>
		<!-- validation-handler param: js function name -->
		<constraint type="MANDATORY"
			validation-handler="Alfresco.forms.validation.exampleGrossValidation"
			event="keyup" />
	</constraint-handlers>
</field>

Alfresco.forms.validation.exampleGrossValidation is the name of js validation
function.
3. exampleFormValidation.js and exampleFormValidation-min.js go to/opt/alfresco-3.4.d/tomcat/webapps/share/components/form

<pre class="brush: javascript; gutter: true">Alfresco.forms.validation.exampleGrossValidation = function exampleGrossValidation(field, args,
  event, form, silent, message) {
 

  var valid = true;

  valid = YAHOO.lang.trim(field.value).length !== 0;  // check if field is not empty

// referencing to form fields is possible by following convention:
// field object passed to function representing validated field has an object form representing the whole form  
// field object names are created by concating 'prop_'+{namespace from data model}_+{property name from data model}  
  var net = field.form.prop_ex_net.value;
  var gross = field.form.prop_ex_gross.value;
  var rate = field.form.prop_ex_rate.value;

  var check = ((rate/100) + 1) * net;

  if((Math.abs(gross - check)) &gt; 0.01)  // check if gross has a valid value with given precision
{
valid = false;
}

  return valid;
};

 
4. exampleValidation_pl_PL.properties (labels for forms) goes to/opt/alfresco-3.4.d/tomcat/webapps/share/WEB-INF/classes/alfresco/messages

You have to modify following files:

1. slingshot-application-context.xml at /opt/alfresco-3.4.d/tomcat/webapps/share/WEB-INF/classes/alfresco/
Paths to share-config-validation-custom.xml and exampleValidation_pl_PL.properties go there
At xPath ‘/beans/bean/constructor-arg/list’ add:

<value>classpath:alfresco/web-extension/share-config-validation-custom.xml</value>
At xPath ‘/beans/bean/property/list’ add:

<value>alfresco.messages.exampleValidation</value>

2. form.get.head.ftl – link to .js fileat /opt/alfresco-3.4.d/tomcat/webapps/share/WEB-INF/classes/alfresco/site-webscripts/org/alfresco/components/form
Add: <@script type=”text/javascript” src=”${page.url.context}/res/components/form/exampleFormValidation.js”></@script>

3. toolbar.get.config.xml – In this file we can add a new option in menu ‘Create content’ in Alfresco Share Site.
at /opt/alfresco-3.4.d/tomcat/webapps/share/WEB-INF/classes/alfresco/site-webscripts/org/alfresco/components/documentlibrary/
add :
<content mimetype=”text/xml” icon=”xml” label=”example.price.menu” itemid=”ex:price”/>