context.set

An alternative to changing individual properties using individual lines you can use the object.set method instead.

set(properties: object, options: object)

object.set(properties [,options]) 

properties - either an object of the same Office.js type on which the method is called or a javascript object with property names and types that mirror the structure of the object.
options - can only be included when you provide a javascript object. The default value is true which is to threw an error if the javascript object includes any read only properties.

var _worksheet = context.workbook.worksheets.getItem("Sheet1"); 
var _range = _worksheet.getRange("A1:B2"); 
_range.set ( { 
   format : { 
      fill : { 
         color : 'AAAAAA'  
         }, 
      font : { 
          name : 'Arial',  
          color : 'white'  
      } 
    } 
});