Table of Contents
1. Overview
What if the binary data is actually a string? For instance, we received a file with textual data.
The build-in TextDecoder object allows to read the value into an actual JavaScript string, given the buffer and the encoding.
We first need to create it:
let decoder = new TextDecoder([label], [options]);
label
– the encoding,utf-8
by default, butbig5
,windows-1251
and many other are also supported.options
– optional object:fatal
– boolean, iftrue
then throw an exception for invalid (non-decodable) characters, otherwise (default) replace them with character\uFFFD
.ignoreBOM
– boolean, iftrue
then ignore BOM (an optional byte-order Unicode mark), rarely needed.
…And then decode:
let str = decoder.decode([input], [options]);
input
–BufferSource
to decode.options
– optional object:stream
– true for decoding streams, whendecoder
is called repeatedly with incoming chunks of data. In that case a multi-byte character may occasionally split between chunks. This options tellsTextDecoder
to memorize “unfinished” characters and decode them when the next chunk comes.
For instance:
let uint8Array = new Uint8Array([72, 101, 108, 108, 111]); alert( new TextDecoder().decode(uint8Array) ); // Hello
let uint8Array = new Uint8Array([228, 189, 160, 229, 165, 189]); alert( new TextDecoder().decode(uint8Array) ); // 你好
We can decode a part of the buffer by creating a subarray view for it:
let uint8Array = new Uint8Array([0, 72, 101, 108, 108, 111, 0]); // the string is in the middle // create a new view over it, without copying anything let binaryString = uint8Array.subarray(1, -1); alert( new TextDecoder().decode(binaryString) ); // Hello
2. TextEncoder
TextEncoder does the reverse thing – converts a string into bytes.
The syntax is:
let encoder = new TextEncoder();
The only encoding it supports is “utf-8”.
It has two methods:
encode(str)
– returnsUint8Array
from a string.encodeInto(str, destination)
– encodesstr
intodestination
that must beUint8Array
.
let encoder = new TextEncoder(); let uint8Array = encoder.encode("Hello"); alert(uint8Array); // 72,101,108,108,111
Related posts:
JavaScript Methods of RegExp and String
JavaScript Methods of primitives
JavaScript BigInt
JavaScript Generators
JavaScript Code structure
JavaScript Moving the mouse: mouseover/out, mouseenter/leave
Resumable file upload
JavaScript Blob
JavaScript Prototype methods, objects without __proto__
JavaScript Functions
JavaScript Anchors: string start ^ and end $
JavaScript Modifying the document
JavaScript Logical operators
JavaScript Strings
JavaScript Promisification
JavaScript Arrow functions revisited
JavaScript Mutation observer
JavaScript Private and protected properties and methods
JavaScript ArrayBuffer, binary arrays
JavaScript The "new Function" syntax
JavaScript DOM tree
JavaScript Error handling, "try...catch"
JavaScript CSS-animations
JavaScript Resource loading: onload and onerror
JavaScript Object methods, "this"
JavaScript Async iteration and generators
JavaScript Object.keys, values, entries
JavaScript Map and Set
JavaScript URL objects
JavaScript Keyboard: keydown and keyup
JavaScript Developer console
Get Started With Node: An Introduction To APIs, HTTP And ES6+ JavaScript