unicode - How to encode a JavaScript string in utf-16?

Unicode - How to encode a JavaScript string in utf-16?

In JavaScript, strings are stored as UTF-16 (16-bit Unicode Transformation Format). JavaScript uses UTF-16 for internal representation of strings, which means that all JavaScript strings are already in UTF-16 encoding when you work with them in your code. However, if you need to explicitly encode or decode strings in UTF-16 for specific operations or interoperability, here are the approaches you can consider:

1. JavaScript String to UTF-16 Byte Array

To convert a JavaScript string to its UTF-16 representation as a byte array, you can use TextEncoder and TextDecoder APIs available in modern browsers. These APIs provide a straightforward way to convert between strings and byte arrays encoded in various formats, including UTF-16.

Encoding a JavaScript String to UTF-16 (Byte Array):

// Example JavaScript string const myString = "Hello, world!"; // Use TextEncoder to encode the string as UTF-16 const encoder = new TextEncoder(); const utf16Bytes = encoder.encode(myString); console.log(utf16Bytes); // Uint8Array representing UTF-16 bytes

Decoding UTF-16 Byte Array back to JavaScript String:

// Example Uint8Array representing UTF-16 bytes const utf16Bytes = new Uint8Array([72, 0, 101, 0, 108, 0, 108, 0, 111, 0, 44, 0, 32, 0, 119, 0, 111, 0, 114, 0, 108, 0, 100, 0, 33, 0]); // Use TextDecoder to decode UTF-16 bytes to string const decoder = new TextDecoder('utf-16'); const decodedString = decoder.decode(utf16Bytes); console.log(decodedString); // Output: "Hello, world!"

2. Manipulating String Data in UTF-16 Format

JavaScript strings are already stored internally as UTF-16, so direct manipulation or processing of strings in JavaScript is typically done in UTF-16 encoding by default.

// Example string with non-BMP (Basic Multilingual Plane) characters const emojiString = "😊"; // Length of string in UTF-16 code units (16-bit units) console.log(emojiString.length); // Output: 2 // Accessing individual UTF-16 code units console.log(emojiString.charCodeAt(0)); // Output: 55357 console.log(emojiString.charCodeAt(1)); // Output: 56842

Notes:

  • Default Encoding: JavaScript strings are UTF-16 encoded by default. You rarely need to manually encode or decode strings unless you are working with specific data formats or interoperability requirements.

  • TextEncoder/TextDecoder: Use TextEncoder and TextDecoder for explicit conversions between JavaScript strings and byte arrays encoded in UTF-16 or other formats.

  • Surrogate Pairs: UTF-16 uses surrogate pairs to represent characters outside the Basic Multilingual Plane (BMP), which is important to consider when working with non-BMP characters like emojis.

By using these methods and understanding how JavaScript handles strings internally, you can effectively work with UTF-16 encoded data as needed in your JavaScript applications.

Examples

  1. How to encode a JavaScript string to UTF-16?

    • Description: This query focuses on converting a JavaScript string to UTF-16 encoding, which is essential for handling Unicode characters that require surrogate pairs.
    • Code:
      let str = "Hello, 你好!"; // Example string let utf16Encoded = unescape(encodeURIComponent(str)); console.log(utf16Encoded); // Outputs the UTF-16 encoded string

  2. How to handle surrogate pairs in JavaScript UTF-16 encoding?

    • Description: This query addresses the proper handling of surrogate pairs when encoding JavaScript strings to UTF-16, ensuring correct representation of characters beyond the BMP (Basic Multilingual Plane).
    • Code:
      function utf16Encode(str) { let utf16Encoded = unescape(encodeURIComponent(str)); return utf16Encoded; } let str = "𐍈"; // Example string with surrogate pair let encoded = utf16Encode(str); console.log(encoded); // Outputs the UTF-16 encoded representation

  3. How to decode a UTF-16 encoded JavaScript string?

    • Description: This query focuses on decoding a UTF-16 encoded JavaScript string back into a readable format, reversing the encoding process.
    • Code:
      function utf16Decode(utf16Encoded) { let decoded = decodeURIComponent(escape(utf16Encoded)); return decoded; } let utf16Encoded = "%uD801%uDC08"; // Example UTF-16 encoded string let decodedStr = utf16Decode(utf16Encoded); console.log(decodedStr); // Outputs the decoded JavaScript string

  4. How to check if a JavaScript string is UTF-16 encoded?

    • Description: This query explores methods to determine if a given JavaScript string is already UTF-16 encoded, useful for validation or conditional processing.
    • Code:
      function isUtf16Encoded(str) { try { decodeURIComponent(escape(str)); return true; } catch (e) { return false; } } let str = "%u0048%u0065%u006C%u006C%u006F"; // Example UTF-16 encoded string console.log(isUtf16Encoded(str)); // Outputs true or false

  5. How to handle non-BMP characters in JavaScript UTF-16 encoding?

    • Description: This query addresses techniques for correctly handling characters outside the BMP (Basic Multilingual Plane) when encoding strings to UTF-16 in JavaScript.
    • Code:
      function utf16Encode(str) { let utf16Encoded = unescape(encodeURIComponent(str)); return utf16Encoded; } let astralSymbol = "𐍈"; // Example astral symbol (U+10408) let encoded = utf16Encode(astralSymbol); console.log(encoded); // Outputs the UTF-16 encoded representation

  6. How to convert a JavaScript string to Little Endian UTF-16 encoding?

    • Description: This query focuses on converting a JavaScript string to UTF-16 Little Endian encoding, often used in certain data formats or protocols.
    • Code:
      function utf16LEEncode(str) { let utf16Encoded = unescape(encodeURIComponent(str)); let result = ""; for (let i = 0; i < utf16Encoded.length; i += 2) { result += utf16Encoded.charAt(i + 1) + utf16Encoded.charAt(i); } return result; } let str = "Hello, 你好!"; // Example string let leEncoded = utf16LEEncode(str); console.log(leEncoded); // Outputs the Little Endian UTF-16 encoded string

  7. How to handle encoding errors when UTF-16 encoding JavaScript strings?

    • Description: This query explores techniques to handle and manage errors that may occur during UTF-16 encoding of JavaScript strings, ensuring robust error handling.
    • Code:
      function utf16EncodeSafe(str) { try { let utf16Encoded = unescape(encodeURIComponent(str)); return utf16Encoded; } catch (e) { console.error("Error encoding to UTF-16:", e); return null; } } let str = "Hello, 你好!"; let encoded = utf16EncodeSafe(str); if (encoded !== null) { console.log(encoded); // Outputs the UTF-16 encoded string }

  8. How to convert a UTF-16 encoded JavaScript string to ASCII?

    • Description: This query focuses on converting a UTF-16 encoded JavaScript string back to ASCII format, which may involve lossy conversion for non-ASCII characters.
    • Code:
      function utf16ToAscii(utf16Encoded) { let asciiEncoded = decodeURIComponent(escape(utf16Encoded)); return asciiEncoded; } let utf16Str = "%u0048%u0065%u006C%u006C%u006F"; // Example UTF-16 encoded string let asciiStr = utf16ToAscii(utf16Str); console.log(asciiStr); // Outputs the ASCII decoded string

  9. How to convert a UTF-16 JavaScript string to UTF-8?

    • Description: This query explores methods to convert a UTF-16 encoded JavaScript string to UTF-8 encoding, which is commonly used for web content.
    • Code:
      function utf16ToUtf8(utf16Encoded) { let utf8Encoded = decodeURIComponent(escape(utf16Encoded)); return utf8Encoded; } let utf16Str = "%u0048%u0065%u006C%u006C%u006F"; // Example UTF-16 encoded string let utf8Str = utf16ToUtf8(utf16Str); console.log(utf8Str); // Outputs the UTF-8 decoded string

  10. How to handle different endianness in JavaScript UTF-16 encoding?

    • Description: This query addresses techniques for managing and handling different endianness (Big Endian and Little Endian) when encoding JavaScript strings to UTF-16.
    • Code:
      function utf16Encode(str, littleEndian = false) { let utf16Encoded = unescape(encodeURIComponent(str)); if (littleEndian) { let result = ""; for (let i = 0; i < utf16Encoded.length; i += 2) { result += utf16Encoded.charAt(i + 1) + utf16Encoded.charAt(i); } return result; } return utf16Encoded; } let str = "Hello, 你好!"; // Example string let leEncoded = utf16Encode(str, true); // Little Endian UTF-16 encoding let beEncoded = utf16Encode(str); // Big Endian UTF-16 encoding console.log("Little Endian:", leEncoded); console.log("Big Endian:", beEncoded);

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