code: function(newMode) {
      if (newMode == 'SPLIT') {
        this.outputConnection.setCheck('Array');
        this.getInput('INPUT').setCheck('String');
      } else {
        this.outputConnection.setCheck('String');
        this.getInput('INPUT').setCheck('Array');
      }
    }
docs: Modify this block to have the correct input and output types.
  @param {string} newMode Either 'SPLIT' or 'JOIN'.
  @private
  @this Blockly.Block