Being fast and light: Using binary data to optimise libraries on the client and the server.

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However, because they recently landed in the JavaScript world, sometimes they are misinterpreted or misused. Semantically, an ArrayBuffer is simply an array of bytes viewed through a specific mask. This mask, an instance of ArrayBufferViewdefines how bytes are aligned to match the expected structure of the content. For example, if you know that the bytes in an ArrayBuffer represent an array of bit unsigned integers, you just wrap the ArrayBuffer in a Uint16Array view and you can manipulate its elements using the brackets syntax as if the Uint16Array was an integer array:.

One common practical question about ArrayBuffer is how to convert a String to an ArrayBuffer and vice-versa. Since an ArrayBuffer is, in fact, a byte array, this conversion requires that both ends agree on how to represent the characters in the String as bytes. You probably have seen this "agreement" before: Thus, supposing you and the other party have agreed on the UTF encoding, the receiving binary data using javascript typed arrays code could be something like:.

Note the use of Uint16Array. This is an ArrayBuffer view that aligns bytes of the ArrayBuffers as bit elements. It doesn't handle the character encoding itself, which is handled as Unicode by String.

A popular StackOverflow question about this has a highly voted answer with a somewhat convoluted solution to the conversion: Although this method works, it has poor readability and I suspect it is slow.

Since unfounded suspicions have driven many mistakes in the history of humanity, let's take a more scientific approach here. I have jsperf'ed the two methods and the result confirms my suspicion and you check out the demo here. Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 3. For details, see our Site Policies. Last updated January 3, Be there and be square. Why Should You Care? A Memory-Saving Experiment Using the web app manifest to specify a site wide theme colour Using the web app manifest to create a solid color loading screen Using requestIdleCallback The larger-than advanced Network Panel filter, and a few others DevTools Digest: Film strip and a new home for throttling Interact with Bluetooth devices on the Web Add a new custom device as a preset MediaStream Deprecations Media playback notifications for Chrome on Android Measuring Performance in a Service Worker Using rotationAngle and touchRadius Inspect and trigger CSS media queries Shortcut to select the next occurrence Select and execute a block of code in the Sources Panel Set a breakpoint based on a certain condition Quickly cycle through receiving binary data using javascript typed arrays DevTools panels Print out a quick stack trace from the Console Who inspects the inspector?

Receiving binary data using javascript typed arrays Dev Summit Let's build some apps with Polymer! Platforms Summary Chrome Dev Summit: Performance Summary Chrome Dev Summit: Polymer declarative, encapsulated, reusable components Chrome Dev Summit: Flexbox layout isn't slow September DevTools answers: What font receiving binary data using javascript typed arrays that?

Stacking Changes Coming to position: Receiving binary data using javascript typed arrays I got your attention?

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JavaScript typed arrays are array-like objects and provide a mechanism for accessing raw binary data. As you may already know, Array objects grow and shrink dynamically and can have any JavaScript value.

JavaScript engines perform optimizations so that these arrays are fast. However, as web applications become more and more powerful, adding features such as audio and video manipulation, access to raw data using WebSockets, and so forth, it has become clear that there are times when it would be helpful for JavaScript code to be able to quickly and easily manipulate raw binary data in typed arrays. However, typed arrays are not to be confused with normal arrays, as calling Array.

Moreover, not all methods available for normal arrays are supported by typed arrays e. To achieve maximum flexibility and efficiency, JavaScript typed arrays split the implementation into buffers and views.

A buffer implemented by the ArrayBuffer object is an object representing a chunk of data; it has no format to speak of and offers no mechanism for accessing its contents.

In order to access the memory contained in a buffer, you need to use a view. A view provides a context — that is, a data type, starting offset, and the number of elements — that turns the data into a typed array. The ArrayBuffer is a data type that is used to represent a generic, fixed-length binary data buffer. You can't directly manipulate the contents of an ArrayBuffer ; instead, you create a typed array view or a DataView which represents the buffer in a specific format, and use that to read and write the contents of the buffer.

Typed array views have self-descriptive names and provide views for all the usual numeric types like Int8 , Uint32 , Float64 and so forth. There is one special typed array view, the Uint8ClampedArray.

It clamps the values between 0 and This is useful for Canvas data processing , for example. This is useful when dealing with different types of data, for example. Typed array views are in the native byte-order see Endianness of your platform. With a DataView you are able to control the byte-order. At this point, we have a chunk of memory whose bytes are all pre-initialized to 0.

There's not a lot we can do with it, though. We can confirm that it is indeed 16 bytes long, and that's about it:.

Before we can really work with this buffer, we need to create a view. Let's create a view that treats the data in the buffer as an array of bit signed integers:. This fills out the 4 entries in the array 4 entries at 4 bytes each makes 16 total bytes with the values 0, 2, 4, and 6. Things start to get really interesting when you consider that you can create multiple views onto the same data. For example, given the code above, we can continue like this:. Here we create a bit integer view that shares the same buffer as the existing bit view and we output all the values in the buffer as bit integers.

Now we get the output 0, 0, 2, 0, 4, 0, 6, 0. The output from this is "Entry 0 in the bit array is now 32". In other words, the two arrays are indeed simply viewed on the same data buffer, treating it as different formats. You can do this with any view types. By combining a single buffer with multiple views of different types, starting at different offsets into the buffer, you can interact with data objects containing multiple data types.

This lets you, for example, interact with complex data structures from WebGL , data files, or C structures you need to use while using js-ctypes. After processing a typed array, it is sometimes useful to convert it back to a normal array in order to benefit from the Array prototype. This can be done using Array. Get the latest and greatest from MDN delivered straight to your inbox. Please check your inbox or your spam filter for an email from us.

The data structure alignment in a C structure is platform-dependent. Take precautions and considerations for these padding differences. The compatibility table on this page is generated from structured data.

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