Blob objects are used to represent immutable, raw data. They are introduced in ECMAScript 2015 and are used to store binary data, blobs, and other large amounts of data that are not suitable for plain text. With the new Blob JavaScript, developers can work with a more efficient and robust way of handling unstructured and large data sets.
In this article, we will explore the Blob object in detail, its properties, methods, and the new features that make it an essential JavaScript tool. We will also demonstrate how to implement Blob objects with code examples.
What is Blob?
A Blob is a file-like object in JavaScript used to store and transmit data. It is composed of a binary or text data set and can be of any size. A Blob object can contain several different types of data such as:
- JSON data
- Text data
- Binary data
- Image data
- Audio data
- Video data
Creating a Blob
To create a Blob object, we use the Blob() constructor. The Blob constructor can take a range of parameters. The simplest constructor takes an array of Buffers or a single Buffer. Here is an example:
const myBuffer = Buffer.from('Hello World', 'utf8');
const myBlob = new Blob([myBuffer]);
In the example above, we create a Buffer from a string that says Hello World in utf8 format. We then pass that Buffer to the Blob constructor and pass the resulting Blob object to myBlob.
The Blob constructor can also be used with other parameters, such as an array of Blobs, an object of options, or an array of data types. Here's an example of using the Blob constructor with an array of Blobs:
const blob1 = new Blob(['This is', ' a']);
const blob2 = new Blob(['sample', ' text']);
const myBlob = new Blob([blob1, blob2], { type: 'text/plain' });
In this example, we create two Blobs using the new Blob constructor and pass them into an array to create a new Blob object. We also pass an options object to define the MIME type of the Blob object.
Properties of a Blob
The Blob object has several properties, including:
- size: The size of the Blob object in bytes.
- type: The Mime type of the Blob object.
Here is an example of using properties in a Blob object:
const myBlob = new Blob(['Hello World'], {type: 'text/plain'});
console.log(`Size of myBlob: ${myBlob.size} bytes`);
console.log(`Type of myBlob: ${myBlob.type}`);
In this example, we create a Blob object using the new Blob constructor with a string of text and a type of "text/plain." We then log out the size and type properties to the console.
Methods of a Blob
The Blob object also has several methods that allow you to work with the data stored within it:
- slice(): Returns a new Blob object containing a subset of the original Blob object.
- arrayBuffer(): Returns a Promise that resolves with an ArrayBuffer containing the data of the Blob object.
- text(): Returns a Promise that resolves with a string containing the data of the Blob object.
- stream(): Returns a ReadableStream object that can be used to read the data of the Blob object.
Here is an example of using the slice() method to create a new Blob object from a subset of the data in an existing Blob object:
const myBlob = new Blob(['This is a sample text'], {type: 'text/plain'});
const newBlob = myBlob.slice(5, 10);
console.log(`New Blob content: ${await newBlob.text()}`);
In this code example, we create a new Blob by slicing the original Blob object to include only the text between the fifth and tenth characters. We then log out the content of the new Blob object to the console using the text() method.
The arrayBuffer(), text(), and stream() methods are also useful for handling different types of data in a Blob object.
Cross-Origin Resource Sharing (CORS)
When loading an external resource, such as an image or audio file, the browser makes a request to a remote server. If the server hosting the file is different from the server hosting the current web page, then the browser considers it as a cross-origin request.
Modern web browsers implement a security mechanism called Cross-Origin Resource Sharing (CORS), which restricts access to resources from other domains. The security restrictions applied by CORS can affect the way Blob objects are created.
For instance, a new Blob object created from content in a different domain's web page will inherit that web page's domain origin. If the Blob object contains data from a different domain, the browser will not allow JavaScript to access that data unless the server providing the data enables CORS headers.
Conclusion
The new Blob JavaScript is a powerful tool that allows for efficient handling of binary and text data sets. Blob objects can be created with a range of parameters and have several properties and methods that facilitate working with large data sets. Blob objects are useful when working with cross-domain resources like images, audio files, video files and more. With the options to slice, extract and customize the data, the Blob object is a great addition to any industry or project that utilizes JavaScript.
- Creating a Blob
The Blob constructor can take several different data types as its input. The simplest way to create a Blob is with an array of Buffers or a single Buffer. Here's an example:
const myBuffer = Buffer.from('Hello World', 'utf8');
const myBlob = new Blob([myBuffer]);
In this example, we create a Buffer from a string that says Hello World in utf8 format. We then pass that Buffer to the Blob constructor and pass the resulting Blob object to myBlob.
The Blob constructor can also be used with other parameters, such as an array of Blobs, an object of options, or an array of data types. Here's an example of using the Blob constructor with an array of Blobs:
const blob1 = new Blob(['This is', ' a']);
const blob2 = new Blob(['sample', ' text']);
const myBlob = new Blob([blob1, blob2], { type: 'text/plain' });
In this example, we create two Blobs using the new Blob constructor and pass them into an array to create a new Blob object. We also pass an options object to define the MIME type of the Blob object.
- Properties of a Blob
The Blob object has two main properties: size and type. The size property returns the size of the Blob object in bytes, while the type property returns the Mime type of the Blob object.
const myBlob = new Blob(['Hello World'], { type: 'text/plain' });
console.log(`Size of myBlob: ${myBlob.size} bytes`);
console.log(`Type of myBlob: ${myBlob.type}`);
- Methods of a Blob
The Blob object has several methods that allow you to work with the data stored within it:
- slice(): Returns a new Blob object containing a subset of the original Blob object.
- arrayBuffer(): Returns a Promise that resolves with an ArrayBuffer containing the data of the Blob object.
- text(): Returns a Promise that resolves with a string containing the data of the Blob object.
- stream(): Returns a ReadableStream object that can be used to read the data of the Blob object.
Here's an example of using the slice() method to create a new Blob object from a subset of the data in an existing Blob object:
const myBlob = new Blob(['This is a sample text'], {type: 'text/plain'});
const newBlob = myBlob.slice(5, 10);
console.log(`New Blob content: ${await newBlob.text()}`);
In this example, we create a new Blob by slicing the original Blob object to include only the text between the fifth and tenth characters. We then log out the content of the new Blob object to the console using the text() method.
The arrayBuffer(), text(), and stream() methods are also useful for handling different types of data in a Blob object.
- Cross-Origin Resource Sharing (CORS)
Cross-Origin Resource Sharing (CORS) is a security mechanism implemented by modern web browsers that restricts access to resources from other domains. The security restrictions applied by CORS can affect the way Blob objects are created.
For instance, a new Blob object created from content in a different domain's web page will inherit that web page's domain origin. If the Blob object contains data from a different domain, the browser will not allow JavaScript to access that data unless the server providing the data enables CORS headers.
In summary, the Blob JavaScript object is a powerful tool for handling unstructured and large data sets. Its various methods and properties make it easy to work with different types of data, and its compatibility with different data types makes it versatile for use in different industries. However, developers must be aware of potential CORS issues when working with Blob objects containing data from different domains.
Popular questions
-
What is Blob in JavaScript?
Answer: A Blob is a file-like object in JavaScript used to store and transmit data. It is composed of a binary or text data set and can be of any size. -
How can you create a Blob in JavaScript?
Answer: To create a Blob object, we use the Blob() constructor. The Blob constructor can take several different data types as its input, such as an array of buffers or Blobs, an object of options, or an array of data types. -
What are the properties of a Blob object?
Answer: The two main properties of a Blob object are size and type. The size property returns the size of the Blob object in bytes, while the type property returns the Mime type of the Blob object. -
What methods are available for working with Blob objects?
Answer: The Blob object has several methods that allow you to work with the data stored within it, such as slice(), arrayBuffer(), text(), and stream(). -
What is Cross-Origin Resource Sharing (CORS) and how does it affect Blob objects?
Answer: Cross-Origin Resource Sharing (CORS) is a security mechanism implemented by modern web browsers that restricts access to resources from other domains. The security restrictions applied by CORS can affect Blob objects containing data from different domains. If the Blob object contains data from a different domain, the browser will not allow JavaScript to access that data unless the server providing the data enables CORS headers.
Tag
Blobscript
