Function complains about an undefined value

Question

When I try to persist my JavaScript object to DynamoDB using the PutCommand, I am seeing the following error message:

Error: Pass options.removeUndefinedValues=true to remove undefined values from map/array/set.

This happens when I use DynamoDBDocumentClient

When I use DynamoDBClient then I must first marshal the object using marshall(..) from @aws-sdk/util-dynamodb. In this case the error is shown when I try to marshal the object.

When I print my object to the console, I don't see any undefined values. However, I don't see the complete object due to too many levels of nesting:

{ id: 123, child: { anotherChild: { nested: [Object] } } }

So instead I use JSON.stringify(..) to display the entire object:

{
    "id": 123,
    "child": {
        "anotherChild": {
            "nested": {
                "name": "Jane"
            }
        }
    }
}

I apparently don't have any undefined attributes, so why am I seeing the error message?

Answer 1

The marshal(..) function will throw this error if it encounters an attribute that is undefined.

marshall({
    name: "John",
    age: undefined,
})

My object did have an undefined value, but it turns out that JSON.stringify(..) will remove attributes with an undefined value.

I had to add a "replacer function" to JSON.stringify(..) to see (and fix) the undefined value.

import {marshall} from "@aws-sdk/util-dynamodb";

const myObject = {
    id: 123,
    child: {
        anotherChild: {
            nested: {
                name: "Jane",
                age: undefined,
            },
        },
    },
};

// Doesn't show the undefined value (too many levels of nesting)
console.log(myObject);

// Doesn't show the undefined value (silently removes undefined attributes)
console.log(JSON.stringify(myObject));

// DOES show the undefined value
console.log(JSON.stringify(myObject, (k, v) => v === undefined ? "!!! WARNING UNDEFINED" : v));

// The marshall function throws an error due to the presence of an undefined attribute
marshall(myObject);