Blob là gì

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The Blob object represents a blob, which is a file-like object of immutable, raw data; they can be read as text or binary data, or converted inkhổng lồ a ReadableStream so its methods can be used for processing the data.

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Blobs can represent data that isn"t necessarily in a JavaScript-native sầu format. The File interface is based on Blob, inheriting blob functionality & expanding it to lớn tư vấn files on the user"s system.


To construct a Blob from other non-blob objects và data, use the Blob() constructor. To create a blob that contains a subphối of another blob"s data, use the slice() method. To obtaina Blob object for a tệp tin on the user"s file system, see the File documentation.

The APIs accepting Blob objects are also listed in the File documentation.


Blob() Returns a newly created Blob object which contains a concatenation of all of the data in the array passed into lớn the constructor.

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Blob.prototype.kích cỡ Read only The size, in bytes, of the data contained in the Blob object. Blob.prototype.type Read only A string indicating the MIMEtype of the data contained in the Blob. If the type is unknown, this string is empty.
Blob.prototype.arrayBuffer() Returns a promise that resolves with an ArrayBuffer containing the entire contents of the Blob as binary data. Blob.prototype.slice() Returns a new Blob object containing the data in the specified range of bytes of the blob on which it"s called. Blob.prototype.stream() Returns a ReadableStream that can be used khổng lồ read the contents of the Blob. Blob.prototype.text() Returns a promise that resolves with a USVString containing the entire contents of the Blob interpreted as UTF-8 text.

The Blob() constructor can create blobs from other objects. For example, khổng lồ construct a blob from a JSON string:


const obj = hello: "world";const blob = new Blob(, type : "application/json");
The following code creates a JavaScript typed array & creates a new Blob containing the typed array"s data. It then calls URL.createObjectURL() lớn convert the blob inkhổng lồ a URL.

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HTML

p>This example creates a typed array containing the ASCII codes for the space character through the letter Z, then converts it to lớn an object URL. A link to lớn open that object URL is created. Cliông xã the links khổng lồ see the decoded object URL.p>
JavaScriptThe main piece of this code for example purposes is the typedArrayToURL() function, which creates a Blob from the given typed array and returns an object URL for it. Having converted the data inkhổng lồ an object URL, it can be used in a number of ways, including as the value of the element"s src attribute (assuming the data contains an image, of course).


function typedArrayToURL(typedArray, mimeType) return URL.createObjectURL(new Blob(, type: mimeType))const bytes = new Uint8Array(59);for(let i = 0; i 59; i++) bytes = 32 + i;const url = typedArrayToURL(bytes, "text/plain");const links = document.createElement("a");liên kết.href = url;liên kết.innerText = "mở cửa the array URL";document.body toàn thân.appendChild(link);

One way to lớn read nội dung from a Blob is khổng lồ use a FileReader. The following code reads the content of a Blob as a typed array:


const reader = new FileReader();reader.addEventListener("loadend", () => // reader.result contains the contents of blob as a typed array);reader.readAsArrayBuffer(blob);
Another way lớn read content from a Blob is lớn use a Response. The following code reads the nội dung of a Blob as text: