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Creating a Custom Code Transformer


Neosync supports the ability to write your own custom logic in javascript for a transformer. We call this the transform_javascript transformer. Custom code transformers take in an input value at the value keyword and execute your custom code against that value. Custom code transformers are also only available for sync jobs since they require an input value.

Creating a Custom Code Transformer

In order to create a custom code transformer:

  1. Navigate to the Transformers page and click on + New Transformer.
  2. You'll be brought to the new transformer page where you can select a base transformer. A base transformer serves as the blueprint for the user defined transformer. Select the Transform Javascript transformer.


  1. Give your transformer a Name and a Description.
  2. Then move onto to the Custom Code section. Here you can write in custom javascript code to transform your input value. Note that the value that you will be transforming is available at the value keyword and is of any type. For example, if the input value was john of type string then the following code:
return value + 'test';

You can also do more complicated transformations such as:

function manipulateString(str) {
let result = reverseString(str);

result = capitalizeString(result);

return result;
// capitalize the string
function capitalizeString(s) {
return s.toUpperCase();
// reverse the string
function reverseString(s) {
return s.split('').reverse().join('');

const input = manipulateString(value);

return input;

This would return johntest. The code editor comes with autocomplete for most standard methods and syntax highlighting. Lastly, we do not currently support module imports in this section. Important: make sure you include a return statement or the custom function will not return a value.

  1. Once you are satisfied with your custom code, click on the Validate button to ensure that your javascript compiles and is valid. If it does not compile, we will return an invalid error. valid
  2. Once your code has compiled, click on Submit to save your custom code transformer. You can now use your custom code transformer in sync jobs.

Creating Column Dependencies

The Custom Code Transformer also allows you to condition a value on a value from another column. Let's take a look at a basic example.

Let's say that we have a table with three fields: id, age, shouldDouble and with types uuid, integer, bool respectively. And we want to create a function that will check the value in the shouldDouble column and if it's true, we want to double the value in the age column. Our code would look something like this:

function doubleAge(age, shouldDouble) {
if (shouldDouble) {
return age * 2;
} else {
return age;

return doubleAge(value, input.shouldDouble);

The key thing to point out here is the input.shouldDouble argument we're passing into the return doubleAge(...) function. We can use the input.{column_name} notation to access values from other columns.

For example, if we had a table that looked like this:


Our output to the age column would be: 40

Things to watch out for


There are a few thing to watch out for as you're writing your custom code. One is that interpolations are a work in progress. For example:

const iam = 'I am';
const five = 5;
return `${iam} ${five}`;

Won't work appropriately since the underlying system we use to compile and run the javascript doesn't recognize that. Instead you would have to do something like:

const iam = 'I am';
const five = 5;
return hello + five.toString();

Calling the toString() method on the integer in order to return it correctly. We're working on this and will update it once we have a fix.