How to inherit js file in odoo ?

First, you define a template in your module to add your js assets located in static/src/js:

<template id="assets_backend" name="newmodulename assets" inherit_id="web.assets_backend"> 
           <xpath expr="." position="inside"> 
               <script type="text/javascript" src="/newmodulename/static/src/js/custom.js"></script> 
           </xpath>
</template>

Then, in your module's new js file, you extend the widget from default module like this:

odoo.define('newmodulename.newmodulename', function (require){
"use strict";
// require original module JS
var instance = openerp;

// Extend widget
instance.web.form.One2ManyListView.include({
    ....
    your code to override here    
    ....
});

}