Skip to main content

Build a custom generator

8. Object block generator​

This section will write the generator for the object block and will demonstrate how to use statementToCode.

The object block generates code for a JSON Object. It has a single statement input, in which member blocks may be stacked.

This object block has multiple member blocks stacked inside it. The members are called a, b, and c and each has a value.

The generated code looks like this:

{
  "a": true,
  "b": "one",
  "c": 1
}

Get the contents​

We'll use statementToCode to get the code for the blocks attached to the statement input of the object block.

statementToCode does three things:

  • Finds the first block connected to the named statement input (the second argument)
  • Generates the code for that block
  • Returns the code as a string

In this case the input name is 'MEMBERS'.

const statement_members = generator.statementToCode(block, 'MEMBERS');

Format and return​

Wrap the statements in curly brackets and return the code, using the default precedence:

const code = '{\n' + statement_members + '\n}';
return [code, Order.ATOMIC];

Note that statementToCode handles the indentation automatically.

Test it​

Here is the full block generator:

jsonGenerator.forBlock['object'] = function (block, generator) {
  const statementMembers = generator.statementToCode(block, 'MEMBERS');
  const code = '{\n' + statementMembers + '\n}';
  return [code, Order.ATOMIC];
};

Test it by generating code for an object block containing a single member block. The result should look like this:

{
  "test": true
}

Next, add a second member block and rerun the generator. Did the resulting code change? Let's look at the next section to find out why not.