Hexadecimal File API (JavaScript)

hexfile.js

/**
 * hexfile.js by Marc - https://github.com/marcrobledo
 *
 * https://github.com/marcrobledo/acnl-editor
 */

import { saveAs } from 'file-saver'

class HexFile {
	/**
	 * Creates a instance of a Hexadecimal File
	 *
	 * @param {File} source The File to be a Hexadecimal file
	 */
	constructor (source) {
    if (typeof source === 'object' && source.name && source.size) {
      this.file = source
      this.fileName = this.file.name
      this.fileSize = this.file.size
      this.fileType = source.type

      this.fileReader = new FileReader()

      this.fileReader.addEventListener('load', () => {
        this.dataView = new DataView(this.fileReader.result)
      })
      this.fileReader.addEventListener('error', console.error)

      this.fileReader.readAsArrayBuffer(this.file)
		}
	}

	/**
	 * Read a Byte (offset) in Hexadecimal File
	 *
	 * @param {number} pos The offset for read - E.g. 0x22
	 * @return {number}
	 */
	readByte (pos) {
		return this.dataView.getUint8(pos)
	}

	/**
	 * Read various Bytes (offsets) in Hexadecimal File
	 *
	 * @param {number} pos The offset for read - E.g. 0x22
	 * @param {number} nBytes Number of bytes to read
	 * @return {Array<number>}
	 */
	readBytes (pos, nBytes) {
		const bytes = new Array(nBytes)

		for (let i = 0; i < nBytes; i++) {
			bytes[i] = this.readByte(pos + i)
		}

		return bytes
	}
  
	/**
	 * Write a Byte(s) to a offset in Hexadecimal File
	 *
	 * @param {number} pos The offset for write - E.g. 0x22
	 * @param {number} byte Byte to write
	 */
	writeByte (pos, byte) {
		this.dataView.setUint8(pos, byte)
  }

	/**
	 * Save file with FileSaver.js
	 */
	save () {
		let blob

		try {
			blob = new Blob([this.dataView], {
				type: this.fileType
			})
		} catch (err) { // old browser, using BlobBuilder or try again
			console.error(err)

			window.BlobBuilder = window.BlobBuilder || window.WebKitBlobBuilder || window.MozBlobBuilder || window.MSBlobBuilder

			if (err.name === 'TypeError' && window.BlobBuilder) {
				const bb = new BlobBuilder()

				bb.append(this.dataView.buffer)
				blob = bb.getBlob(this.fileType)
			} else if (err.name === 'InvalidStateError') {
				blob = new Blob([this.dataView.buffer], {
					type: this.fileType
				})
			}
		}

		saveAs(blob, this.fileName)
	}
}

export default HexFile