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Overview

The Code Block allows you to run arbitrary JavaScript code during your flow’s execution. This can be useful for a variety of purposes, such as:

  • Performing complex calculations
  • Custom, domain-specific logic that is complex to represent in Lawme blocks alone
  • Using JavaScript functions that are not available in other blocks

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Code Inputs

The inputs to the code block are accessible in the special variable inputs. To access the input named foo, it is accessible on inputs.foo.

All inputs have the following structure:

{
  type: string;
  value: any;
}

The type of each input corresponds to a Data Type. The value is the actual value of the input.

For example, if you have an input named myNumber that is a number, you can access it in the code block like this:

const foo = inputs.myNumber.value; // inputs.myNumber.type === 'number'

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Code Outputs

The code block must return an object containing the output values. Each property of the output object must correspond to one of the configured output names in the editor.

Each of the values of the properties must be an object with the {type: DataType; value: any} structure described above.

For example, if you have an output named myNumber that is a number, you can return it like this:

return {
  myNumber: {
    type: 'number',
    value: 123,
  },
};

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    Example 1: Use .slice to get a substring

    1. Create a Code Block with the following code:

      return {
  output: {
    type: 'string',
    value: inputs.input.value.slice(0, 5),
  },
};

    2. Create a Text block, give it the value Hello World, and connect it to the Code Block’s input port.

    3. Run the flow. Note that the Code Block’s output is Hello.

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    Example 2: Concatenate two strings, and output the length and the string.

    1. Create a Code Block with the following code:

      const concatenated = inputs.input1.value + inputs.input2.value;
return {
  length: {
    type: 'number',
    value: concatenated.length,
  },
  output: {
    type: 'string',
    value: concatenated,
  },
};

    2. Rename the existing input of the Code block to input1, and add a 2nd input to input2. Add a 2nd output named length.

    3. Create two Text blocks, give them the values Hello and World, and connect them to the Code Block’s input1 and input2 ports, respectively.

    4. Run the flow. Note that the Code Block outputs HelloWorld and 10.

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    Error Handling

    If any error happens during the execution of the Code Block, then the block will error.

    If you are unsure of the type of value passed into the code block, for example when reusing it in multiple places, you can and should check the type of the input before using it. For example:

    if (inputs.input.type === 'string') {
  // Do something with inputs.input.value
}

    If you throw an Error in the code block, then it will error.

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    FAQ

    Q: How is the code block implemented?

    A: The Code Block is implemented using a Function constructor with, as of right now, only one argument passed in to it - inputs. This is the same as if you were to write the following code:

    function codeBlock(inputs) {
  // Code here
}

    Q: Can I use async/await in the code block?

    A: No. The code block is executed synchronously, and does not support async/await. As you cannot use external libraries in a Code block, there is no need for async/await support anyway. Use an External Call Block instead.

    Q: Can I use external libraries in the code block?

    A: No. The code block is executed in a sandboxed environment, and does not have access to external libraries. Use an External Call Block instead.

    Q: Can I use console.log in the code block?

    A: No, the console variable is not available in a code block.

    Q: Can the code block function like an If Block?

    A: Yes. If you return the special value { type: 'control-flow-excluded', value: undefined } from the Code block, then the blocks after the Code block will be excluded from the flow’s execution. This is useful if you want to conditionally execute a portion of the flow.

    Q: Is there any timeout? What if I create an infinite loop?

    A: There is no timeout. If you create an infinite loop, then the flow will hang indefinitely.

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    See Also