string.underscore
    string.underscore(s)
  
  
  
  Parameters
- str 
{String}:a string in camelCase
 
Returns
 {String}: 
the supplied string with camelCase converted to underscore-lowercase digraphs
var string = require("can-util/js/string/string");
console.log(string.underscore("fooBar")); // -> "foo_bar"
console.log(string.underscore("HTMLElement")); // -> "html_element"