Inheriting javascript from OpenERP 7 web client

openerp.restaurant_POS = function(instance) {
var module = instance.point_of_sale;
//This will instantiate point_of_sale

module.POSWidget = module.POSWidget.extend({
// Now Extending functionality of POSWidget
// You can add your functions here also you can change functions
// inherited from POSWidget.

//Adding new function
mynewfunc : function(){
console.log(“This is new function”);
},

Step 3: Now to add view add new folder xml to static/src and add new file somenae_view.xml to that folder.

e.g Adding new widget Widget 

<templates id="template" xml:space="preserve">

<t t-name="Widget">
     <div id="screen_name" class="screen" >
         <header><h2>Select</h2></header>
         <div class="POS-step-container">
             <div class="POS-receipt-container">
                 
             </div>
         </div>
     </div>
</t>
</template>


Extending xml view from other module:
If you want to add new button,textfiled or anything to alredy created view then you can extend template.
e.g. Extending  POSWidget and add new button to action bar 

<template>
 <t t-extend="POSWidget">
<t t-jquery=".point-of-sale .placeholder-UsernameWidget" t-operation="after">
<button id="new button name" class="class name" style="background:linear-gradient(#B2B3D7, #7F82AC) repeat scroll 0 0 transparent">Button name</button>
</t>
</t>
</template>

t-operation options: 
after : adding component after the current
before : adding component before the current 

 
Step 4: Add .js filenames and .xml filename to __openERP__.py file.xml files to qweb and .js file to js as

{
 'qweb': [ 'static/src/xml/pos.xml' ,],

  'js': [ 'static/src/js/pos.js',   ],
}