api/transactions.js
function(transaction, _callback) {
      transaction.remote = api.remote;

      if (options.blockDuplicates === true) {
        blockDuplicates(transaction, options, _callback);
      } else {
        _callback(null, transaction);
      }
    }
function(transaction, _callback) {
      transaction.remote = api.remote;

      if (options.blockDuplicates === true) {
        blockDuplicates(transaction, options, _callback);
      } else {
        _callback(null, transaction);
      }
    }
function ( transaction , _callback ) { transaction . remote = api . remote ; if ( options . blockDuplicates === true ) { blockDuplicates ( transaction , options , _callback ) ; } else { _callback ( null , transaction ) ; } }
Duplicate blocking is performed here
Duplicate blocking is performed here