![]() ![]() In many cases though, we don’t have to read the file contents. Data url, base-64 encoded ( readAsDataURL).We usually get File objects from user input, like or Drag’n’Drop events ( ondragend).įileReader objects can read from a file or a blob, in one of three formats: In addition to Blob methods and properties, File objects also have name and lastModified properties, plus the internal ability to read from filesystem. That’s only inside a Web Worker though, because delays in synchronous calls, that are possible while reading from files, in Web Workers are less important. Its reading methods read* do not generate events, but rather return a result, as regular functions do. The most widely used events are for sure load and error.įor Web Workers, there also exists a synchronous variant of FileReader, called FileReaderSync. reader.result is the result (if successful).When the reading is finished, we can access the result as: loadend – reading finished with either success or failure.There’s an alternative to reading a file for that, as discussed in chapter Blob: URL.createObjectURL(file).Īs the reading proceeds, there are events: readAsDataURL – when we’d like to use this data in src for img or another tag.readAsText – for text files, when we’d like to get a string.For high-level operations, like slicing, File inherits from Blob, so we can call them directly, without reading. readAsArrayBuffer – for binary files, to do low-level binary operations. ![]() ![]() The choice of read* method depends on which format we prefer, how we’re going to use the data. readAsDataURL(blob) – read the binary data and encode it as base64 data url.readAsText(blob, ) – read the data as a text string with the given encoding ( utf-8 by default).readAsArrayBuffer(blob) – read the data in binary format ArrayBuffer.Let reader = new FileReader() // no arguments ![]()
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