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The DataView Object

Published May 17 2019

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DataView is a view into an ArrayBuffer, like Typed Arrays, but in this case the items in the array can have different sizes and types.

Here’s an example:

const buffer = new ArrayBuffer(64)
const view = new DataView(buffer)

Since this is a view over a buffer, we can specify which byte we want to start from, and the length:

const view = new DataView(buffer, 10) //start at byte 10

const view = new DataView(buffer, 10, 30) //start at byte 10, and add 30 items

If we don’t add those additional arguments, the view starts at position 0 and loads all the bytes present in the buffer.

There is a set of methods we can use to add data into the buffer:

• setInt8()
• setInt16()
• setInt32()
• setUint8()
• setUint16()
• setUint32()
• setFloat32()
• setFloat64()

This is how to call one of those methods:

const buffer = new ArrayBuffer(64)
const view = new DataView(buffer)
view.setInt16(0, 2019)

By default data is stored using big endian notation. You can overwrite this setting and use little endian by adding a third parameter with the true value:

const buffer = new ArrayBuffer(64)
const view = new DataView(buffer)
view.setInt16(0, 2019, true)

Here is how we can get data from the view:

• getInt8()
• getInt16()
• getInt32()
• getUint8()
• getUint16()
• getUint32()
• getFloat32()
• getFloat64()

Example:

const buffer = new ArrayBuffer(64)
const view = new DataView(buffer)
view.setInt16(0, 2019)
view.getInt16(0) //2019

Since a DataView is an ArrayBufferView, we have those 3 read-only properties:

• buffer points to the original ArrayBuffer
• byteOffset is the offset on that buffer
• byteLength is the length of its content in bytes

One thing to keep in mind is that typed arrays don’t let us control the endianness: it uses the endianness of the system. In general this works out fine, because the main use case as we said is to use the array locally, using one of the multimedia APIs.

If you transfer the data of a Typed Array on another system, the data might be not badly encoded if it uses Big Endian and you use Little Endian.

In case you need this kind of control, DataView is a perfect choice.

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