nodejs Wave File parser

wavr.js

const fs = require('fs');

class WavHeader {
    constructor() {
        this.sGroupId = "";
        this.dwFileLength = 0;
        this.sRiffType = "";
    }
}

class FormatChunk {
    constructor() {
        this.sGroupId = "";
        this.dwChunkSize = 0;
        this.wFormatTag = 0;
        this.wChannels = 0;
        this.dwSamplesPerSec = 0;
        this.dwAvgBytesPerSec = 0;
        this.wBlockAlign = 0;
        this.dwBitsPerSample = 0;
    }
}

class DataChunk {
    constructor() {
        this.sGroupId = "";
        this.dwChunkSize = 0;
        this.sampleData = [];
    }
}

class WavReader {
    constructor(buffer) {
        this.header = null;
        this.format = null;

        this.buffer = buffer;
        this.pos = 0;
    }

    getByte() {
        return this.buffer.readInt8(this.pos++);
    }

    getUInt() {
        const result = this.buffer.readInt32LE(this.pos);
        this.pos += 4;
        return result;
    }

    getUShort() {
        const result = this.buffer.readInt16LE(this.pos);
        this.pos += 2;
        return result;
    }

    getChar() {
        return String.fromCharCode(this.getByte());
    }

    peekChar(offset) {
        return String.fromCharCode(this.buffer.readInt8(this.pos + offset));
    }

    peekToken() {
        return `${this.peekChar(0)}${this.peekChar(1)}${this.peekChar(2)}${this.peekChar(3)}`;
    }

    readToData() {
        while (this.pos <= this.buffer.length) {
            const groupId = this.peekToken();
            if (groupId == "data") break;
            else this.getByte();
        }
    }

    getBlock() {
        // read the first 4 bytes to understand the type
        const groupId = `${this.getChar()}${this.getChar()}${this.getChar()}${this.getChar()}`;
        let chunk = null;

        switch(groupId) {
            case "RIFF":
                chunk = new WavHeader();
                chunk.sGroupId = groupId;
                chunk.dwFileLength = this.getUInt();
                chunk.sRiffType = `${this.getChar()}${this.getChar()}${this.getChar()}${this.getChar()}`;
                this.header = chunk;
            break;

            case "fmt ":
                chunk = new FormatChunk();
                chunk.sGroupId = groupId;
                chunk.dwChunkSize = this.getUInt();
                chunk.wFormatTag = this.getUShort();
                chunk.wChannels = this.getUShort();
                chunk.dwSamplesPerSec = this.getUInt();
                chunk.dwAvgBytesPerSec = this.getUInt();
                chunk.wBlockAlign = this.getUShort();
                chunk.dwBitsPerSample = this.getUInt();
                this.format = chunk;
            break;

            case "data":
                chunk = new DataChunk();
                chunk.sGroupId = groupId;
                chunk.dwChunkSize = this.getUInt();
                chunk.sampleData = this.buffer.slice(this.pos);
                chunk.seconds = chunk.sampleData.length / (this.format.dwSamplesPerSec * this.format.wChannels * (this.format.dwChunkSize / 8));
            break;
        }

        return chunk;
    }

    process() {
        console.log(this.getBlock());
        console.log(this.getBlock());

        // Skip other blocks
        this.readToData();

        // Read the data block
        console.log(this.getBlock());
    }
}

const filePath = "/home/sharpcoder/AmzMusic/late-in-the-evening.wav";
const bytes = fs.readFileSync(filePath);
const reader = new WavReader(bytes);
reader.process();