Function onerror

packages/main/test/pages/diffable-html.js:6713–6718

(er)

      // if the dest has an error, then stop piping into it.
      // however, don't suppress the throwing behavior for this.
      function onerror(er) {
        debug('onerror', er);
        unpipe();
        dest.removeListener('error', onerror);
        if (EElistenerCount(dest, 'error') === 0) dest.emit('error', er);
      }

      // Make sure our error handler is attached before userland ones.
      prependListener(dest, 'error', onerror);