JS Filters Syntax Reference

Introduction

JS filter is used to filter Kafka records. The filter is evaluated on each record on the server. It's powerful and can handle complex filters, but requires writing JavaScript code.

caution

This filter is not the preferred method.
We recommend that you use the simpler and more performant filters: Global Search and Search in a Specific field .

The code has to return a boolean.

If your code returns true, the record will be included in the results.

Otherwise the record will be skipped.

return value.totalPrice >= 30; // Selects all the orders having a total price superior to or equal to 30

Record attributes

When creating JavaScript filters, you may want to access message data or the metadata. See the parameters in the table below for accessing different message attributes.

Attribute	Types
key	Object
value	Object
headers	Object
serializedKeySize	Number
serializedValueSize	Number
keySchemaId	Number
valueSchemaId	Number
offset	Number
partition	Number

Example filters

Let's imagine we have the following 2 Records in our topic:

Record 1:

{
  "key": "order",
  "value": {
    "orderId": 12345,
    "paid": true,
    "totalPrice": 50,
    "items": [
      {
        "id": "9cb5cb81-b678-4f96-84dc-70096038eca9",
        "name": "beers pack"
      },
      {
        "id": "507b5045-eafd-41a6-afb5-1890f08cfd8e",
        "name": "baby diapers pack"
      }
    ]
  },
  "headers": {
    "app": "orders-microservice",
    "trace-id": "9f0f004a-70c5-4301-9d28-bf5d7ebf238d"
  }
}

Record 2:

{
  "key": "order",
  "value": {
    "orderId": 12346,
    "paid": false,
    "totalPrice": 10,
    "items": [
      {
        "id": "7f55662e-5ba2-4ab4-9546-45fdd1ca60ca",
        "name": "shampoo bottle"
      }
    ]
  },
  "headers": {
    "app": "orders-microservice",
    "trace-id": "1076c6dc-bd6c-4d5e-8a11-933b10bd77f5"
  }
}

Here are some examples of filters related to these records:

return value.totalPrice >= 30;
// Selects all the orders having a total price superior to or equal to 30

return value.items.length > 1;
// Selects all the orders containing more than one 1 item

return value.orderId == 12345;
// Finds a specific order based in its ID

return !value.paid;
// Selects all the orders that aren't paid

return !headers.includesKey("trace-id");
// Selects all the records not having a trace-id header

const isHighPrice = value.totalPrice >= 30
const moreThanOneItem = value.items.length > 1
return isHighPrice && moreThanOneItem
// Selects all the orders having a total price superior to or equal to 30 and having more than one 1 item