code: function() {
      this.jsonInit({
        "message0": "%1 %2 %3",
        "args0": [
          {
            "type": "input_value",
            "name": "A",
            "check": "Number"
          },
          {
            "type": "field_dropdown",
            "name": "OP",
            "options":
              [[Blockly.Msg.MATH_ADDITION_SYMBOL, 'ADD'],
               [Blockly.Msg.MATH_SUBTRACTION_SYMBOL, 'MINUS'],
               [Blockly.Msg.MATH_MULTIPLICATION_SYMBOL, 'MULTIPLY'],
               [Blockly.Msg.MATH_DIVISION_SYMBOL, 'DIVIDE'],
               [Blockly.Msg.MATH_POWER_SYMBOL, 'POWER']]
          },
          {
            "type": "input_value",
            "name": "B",
            "check": "Number"
          }
        ],
        "inputsInline": true,
        "output": "Number",
        "colour": Blockly.Blocks.math.HUE,
        "helpUrl": Blockly.Msg.MATH_ARITHMETIC_HELPURL
      });
      // Assign 'this' to a variable for use in the tooltip closure below.
      var thisBlock = this;
      this.setTooltip(function() {
        var mode = thisBlock.getFieldValue('OP');
        var TOOLTIPS = {
          'ADD': Blockly.Msg.MATH_ARITHMETIC_TOOLTIP_ADD,
          'MINUS': Blockly.Msg.MATH_ARITHMETIC_TOOLTIP_MINUS,
          'MULTIPLY': Blockly.Msg.MATH_ARITHMETIC_TOOLTIP_MULTIPLY,
          'DIVIDE': Blockly.Msg.MATH_ARITHMETIC_TOOLTIP_DIVIDE,
          'POWER': Blockly.Msg.MATH_ARITHMETIC_TOOLTIP_POWER
        };
        return TOOLTIPS[mode];
      });
    }
docs: Block for basic arithmetic operator.
  @this Blockly.Block