pdf-lib
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Create and modify PDF files with JavaScript
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TypeScript
/**
* Encodes a string to UTF-8.
*
* @param input The string to be encoded.
* @param byteOrderMark Whether or not a byte order marker (BOM) should be added
* to the start of the encoding. (default `true`)
* @returns A Uint8Array containing the UTF-8 encoding of the input string.
*
* -----------------------------------------------------------------------------
*
* JavaScript strings are composed of Unicode code points. Code points are
* integers in the range 0 to 1,114,111 (0x10FFFF). When serializing a string,
* it must be encoded as a sequence of words. A word is typically 8, 16, or 32
* bytes in size. As such, Unicode defines three encoding forms: UTF-8, UTF-16,
* and UTF-32. These encoding forms are described in the Unicode standard [1].
* This function implements the UTF-8 encoding form.
*
* -----------------------------------------------------------------------------
*
* In UTF-8, each code point is mapped to a sequence of 1, 2, 3, or 4 bytes.
* Note that the logic which defines this mapping is slightly convoluted, and
* not as straightforward as the mapping logic for UTF-16 or UTF-32. The UTF-8
* mapping logic is as follows [2]:
*
* • If a code point is in the range U+0000..U+007F, then view it as a 7-bit
* integer: 0bxxxxxxx. Map the code point to 1 byte with the first high order
* bit set to 0:
*
* b1=0b0xxxxxxx
*
* • If a code point is in the range U+0080..U+07FF, then view it as an 11-bit
* integer: 0byyyyyxxxxxx. Map the code point to 2 bytes with the first 5 bits
* of the code point stored in the first byte, and the last 6 bits stored in
* the second byte:
*
* b1=0b110yyyyy b2=0b10xxxxxx
*
* • If a code point is in the range U+0800..U+FFFF, then view it as a 16-bit
* integer, 0bzzzzyyyyyyxxxxxx. Map the code point to 3 bytes with the first
* 4 bits stored in the first byte, the next 6 bits stored in the second byte,
* and the last 6 bits in the third byte:
*
* b1=0b1110zzzz b2=0b10yyyyyy b3=0b10xxxxxx
*
* • If a code point is in the range U+10000...U+10FFFF, then view it as a
* 21-bit integer, 0bvvvzzzzzzyyyyyyxxxxxx. Map the code point to 4 bytes with
* the first 3 bits stored in the first byte, the next 6 bits stored in the
* second byte, the next 6 bits stored in the third byte, and the last 6 bits
* stored in the fourth byte:
*
* b1=0b11110xxx b2=0b10zzzzzz b3=0b10yyyyyy b4=0b10xxxxxx
*
* -----------------------------------------------------------------------------
*
* It is important to note, when iterating through the code points of a string
* in JavaScript, that if a character is encoded as a surrogate pair it will
* increase the string's length by 2 instead of 1 [4]. For example:
*
* ```
* > 'a'.length
* 1
* > '💩'.length
* 2
* > '語'.length
* 1
* > 'a💩語'.length
* 4
* ```
*
* The results of the above example are explained by the fact that the
* characters 'a' and '語' are not represented by surrogate pairs, but '💩' is.
*
* Because of this idiosyncrasy in JavaScript's string implementation and APIs,
* we must "jump" an extra index after encoding a character as a surrogate
* pair. In practice, this means we must increment the index of our for loop by
* 2 if we encode a surrogate pair, and 1 in all other cases.
*
* -----------------------------------------------------------------------------
*
* References:
* - [1] https://www.unicode.org/versions/Unicode12.0.0/UnicodeStandard-12.0.pdf
* 3.9 Unicode Encoding Forms - UTF-8
* - [2] http://www.herongyang.com/Unicode/UTF-8-UTF-8-Encoding.html
* - [3] http://www.herongyang.com/Unicode/UTF-8-UTF-8-Encoding-Algorithm.html
* - [4] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length#Description
*
*/
export declare const utf8Encode: (input: string, byteOrderMark?: boolean) => Uint8Array;
/**
* Encodes a string to UTF-16.
*
* @param input The string to be encoded.
* @param byteOrderMark Whether or not a byte order marker (BOM) should be added
* to the start of the encoding. (default `true`)
* @returns A Uint16Array containing the UTF-16 encoding of the input string.
*
* -----------------------------------------------------------------------------
*
* JavaScript strings are composed of Unicode code points. Code points are
* integers in the range 0 to 1,114,111 (0x10FFFF). When serializing a string,
* it must be encoded as a sequence of words. A word is typically 8, 16, or 32
* bytes in size. As such, Unicode defines three encoding forms: UTF-8, UTF-16,
* and UTF-32. These encoding forms are described in the Unicode standard [1].
* This function implements the UTF-16 encoding form.
*
* -----------------------------------------------------------------------------
*
* In UTF-16, each code point is mapped to one or two 16-bit integers. The
* UTF-16 mapping logic is as follows [2]:
*
* • If a code point is in the range U+0000..U+FFFF, then map the code point to
* a 16-bit integer with the most significant byte first.
*
* • If a code point is in the range U+10000..U+10000, then map the code point
* to two 16-bit integers. The first integer should contain the high surrogate
* and the second integer should contain the low surrogate. Both surrogates
* should be written with the most significant byte first.
*
* -----------------------------------------------------------------------------
*
* It is important to note, when iterating through the code points of a string
* in JavaScript, that if a character is encoded as a surrogate pair it will
* increase the string's length by 2 instead of 1 [4]. For example:
*
* ```
* > 'a'.length
* 1
* > '💩'.length
* 2
* > '語'.length
* 1
* > 'a💩語'.length
* 4
* ```
*
* The results of the above example are explained by the fact that the
* characters 'a' and '語' are not represented by surrogate pairs, but '💩' is.
*
* Because of this idiosyncrasy in JavaScript's string implementation and APIs,
* we must "jump" an extra index after encoding a character as a surrogate
* pair. In practice, this means we must increment the index of our for loop by
* 2 if we encode a surrogate pair, and 1 in all other cases.
*
* -----------------------------------------------------------------------------
*
* References:
* - [1] https://www.unicode.org/versions/Unicode12.0.0/UnicodeStandard-12.0.pdf
* 3.9 Unicode Encoding Forms - UTF-8
* - [2] http://www.herongyang.com/Unicode/UTF-16-UTF-16-Encoding.html
* - [3] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length#Description
*
*/
export declare const utf16Encode: (input: string, byteOrderMark?: boolean) => Uint16Array;
/**
* Returns `true` if the `codePoint` is within the
* Basic Multilingual Plane (BMP). Code points inside the BMP are not encoded
* with surrogate pairs.
* @param codePoint The code point to be evaluated.
*
* Reference: https://en.wikipedia.org/wiki/UTF-16#Description
*/
export declare const isWithinBMP: (codePoint: number) => boolean;
/**
* Returns `true` if the given `codePoint` is valid and must be represented
* with a surrogate pair when encoded.
* @param codePoint The code point to be evaluated.
*
* Reference: https://en.wikipedia.org/wiki/UTF-16#Description
*/
export declare const hasSurrogates: (codePoint: number) => boolean;
export declare const highSurrogate: (codePoint: number) => number;
export declare const lowSurrogate: (codePoint: number) => number;
/**
* Decodes a Uint8Array of data to a string using UTF-16.
*
* Note that this function attempts to recover from erronous input by
* inserting the replacement character (�) to mark invalid code points
* and surrogate pairs.
*
* @param input A Uint8Array containing UTF-16 encoded data
* @param byteOrderMark Whether or not a byte order marker (BOM) should be read
* at the start of the encoding. (default `true`)
* @returns The decoded string.
*/
export declare const utf16Decode: (input: Uint8Array, byteOrderMark?: boolean) => string;
export declare const hasUtf16BOM: (bytes: Uint8Array) => boolean;
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