Build a custom generator

5. Value block generators

This step will build the generators for the simple value blocks: logic_null, text, math_number, and logic_boolean.

It will use getFieldValue on several types of fields.

Null

The simplest block in this example is the logic_null block.

No matter what, it generates the code 'null'. Notice that this is a string, because all generated code is a string. Add the following code to src/generators/json.js:

jsonGenerator.forBlock['logic_null'] = function (block) {
  return ['null', Order.ATOMIC];
};

String

Next is the text block.

Unlike logic_null, there is a single text input field on this block. Use getFieldValue:

const textValue = block.getFieldValue('TEXT');

Since this is a string in the generated code, wrap the value in quotation marks and return it:

jsonGenerator.forBlock['text'] = function (block) {
  const textValue = block.getFieldValue('TEXT');
  const code = `"${textValue}"`;
  return [code, Order.ATOMIC];
};

Number

The math_number block has a number field.

Like the text block, the math_number block can use getFieldValue. Unlike the text block, the function doesn't need to wrap it in additional quotation marks, because in the JSON code, it won't be a string.

However, like all generated code and as with null above, the function needs to return the code as a string from the generator.

jsonGenerator.forBlock['math_number'] = function (block) {
  const code = String(block.getFieldValue('NUM'));
  return [code, Order.ATOMIC];
};

Boolean

The logic_boolean block has a dropdown field named BOOL.

Calling getFieldValue on a dropdown field returns the value of the selected option, which may not be the same as the display text. In this case the dropdown has two possible values: TRUE and FALSE.

jsonGenerator.forBlock['logic_boolean'] = function (block) {
  const code = block.getFieldValue('BOOL') === 'TRUE' ? 'true' : 'false';
  return [code, Order.ATOMIC];
};

Summary

• Value blocks return an array containing the value as a string and the precedence.
• getFieldValue finds the field with the specified name and returns its value.
• The type of the return value from getFieldValue depends on the type of the field.
• Each field type must document what its value represents.