gistfile1.js

// api 
var api_url = 'http://api.knackhq.com/v1/objects/object_1/records';

// preparing filters
var filters = [
  {
    field: 'field_1',
    operator: 'is',
    value: 'test'
  },
  {
    field: 'field_2',
    operator: 'is not blank'
  }
]

// add to URL
api_url += '?filters=' encodeURIComponent(JSON.stringify(filters));