Stream writable.writableObjectMode Property in Node.js

The writable.writableObjectMode property in Node.js reveals whether a writable stream has been configured to work in object mode. In object mode, streams handle JavaScript values other than just buffers or strings — like numbers, booleans, or even objects.

What Is writableObjectMode?

This property returns a Boolean value. If it's true, the stream can write arbitrary JavaScript values. If false, only buffers and strings are allowed. It’s a read-only property that helps you inspect the internal mode of a stream.

Syntax

writable.writableObjectMode

This is a simple property that doesn’t require any arguments. You can use it to check if a stream supports object writing.

Why Use Object Mode?

Object mode is useful when working with non-binary data — for example, streaming structured data like JSON objects or database rows. It allows streams to pass along full JavaScript objects rather than converting them to strings or buffers.

Example: Checking writableObjectMode

Here's a quick demonstration of how to check whether a stream is in object mode:

const { Writable } = require('stream');

const objStream = new Writable({
    objectMode: true,
    write(chunk, encoding, callback) {
        console.log('Received object:', chunk);
        callback();
    }
});

console.log('Is object mode?', objStream.writableObjectMode); // true
    

In this example, since objectMode is set to true, the stream is able to accept full JavaScript objects.

Use Cases

• Streaming API responses in object form
• Passing structured data between processes
• Transforming or filtering data objects in a pipeline

Important Points

• This is a read-only property — you must set object mode during stream creation.
• Attempting to write objects to a non-object mode stream will throw an error.
• Object mode applies separately to readable and writable sides in duplex streams.

Conclusion

The writable.writableObjectMode property in Node.js is a simple yet valuable indicator that helps determine whether a writable stream can handle JavaScript objects. It’s especially useful when designing custom streams that need to work with complex data types beyond just text or binary data.