Some types of compression in js

LZW.js

(() => {
    const fcp = String.fromCodePoint;
    const L = "length";
    /**
     * @param {Uint8Array} input
     * @returns {Uint8Array}
     */
    function compress(input) {
        const codewords = [];
        const dictionary = new Map();
        for (let i = 0; i < 256; i++)
            dictionary.set(fcp(i), i);
        let buf = "", next = "", bufnext = "";
        for (let x of input) {
            next = fcp(x);
            bufnext = buf + next;
            if (dictionary.has(bufnext))
                buf = bufnext;
            else {
                codewords.push(dictionary.set(bufnext, dictionary.size).get(buf));
                buf = next;
            }
        }
        codewords.push(dictionary.get(buf));
        return ((input) => {
            /**
             * Condenses a byte array into an array of numbers.
             * @param {Uint32Array} input
             * @returns {Uint8Array}
             */
            const max = input.reduce((p = 0, n) => n > p ? n : p);
            const bits = 1 + Math.floor(Math.log2(max));
            const output = new Uint8Array(1 + 4 + Math.ceil(input[L] * bits / 8));
            output[0] = bits;
            for (let i = 0; i < 4; i++)
                output[1 + i] = (input[L] >> (i * 8)) & 0xff;
            for (let i = 0; i < input[L]; i++)
                for (let j = 0; j < bits; j++) {
                    const k = 8 * 5 + (i * bits + j);
                    output[k >> 3] |= (1 << ((k % 8))) * ((input[i] >> j) & 1);
                }
            return output;
        })(codewords);
    }
    /**
     * @param {Uint8Array} input
     * @returns {Uint8Array}
     */
    function decompress(input) {
        const codewords = ((input) => {
            /**
             * Uncondenses a byte array into an array of numbers.
             * @param {Uint8Array} input
             * @returns {Uint32Array}
             */
            const bits = input[0];
            const length = input.slice(1, 5).reverse().reduce((p, n) => (p << 8) | n, 0);
            const output = new Uint32Array(length);
            for (let i = 0; i < input[L]; i++)
                for (let j = 0; j < bits; j++) {
                    const k = 8 * 5 + (i * bits + j);
                    output[i] |= (1 << j) * ((input[k >> 3] >> (k % 8)) & 1);
                }
            return output;
        })(input);
        const dictionary = [];
        for (let i = 0; i < 256; i++)
            dictionary.push(fcp(i));
        let prev = dictionary[codewords[0]], next = "";
        const values = [prev];
        for (let k of codewords.slice(1)) {
            values.push(next = k < dictionary[L] ? dictionary[k] : prev + prev[0]);
            dictionary.push(prev + next[0]);
            prev = next;
        }
        const output = [];
        for (let c of values.join(""))
            output.push(c.codePointAt(0));
        return new Uint8Array(output);
    }
    return { compress, decompress };
})()

LZW.min.js

(()=>{const t=String.fromCodePoint,e="length";return{compress:(o)=>{const r=[],n=new Map;for(let e=0;e<256;e++)n.set(t(e),e);let s="",c="",l="";for(let e of o)l=s+(c=t(e)),n.has(l)?s=l:(r.push(n.set(l,n.size).get(s)),s=c);return r.push(n.get(s)),(t=>{const o=t.reduce((t=0,e)=>e>t?e:t),r=1+Math.floor(Math.log2(o)),n=new Uint8Array(5+Math.ceil(t[e]*r/8));n[0]=r;for(let o=0;o<4;o++)n[1+o]=t[e]>>8*o&255;for(let o=0;o<t[e];o++)for(let e=0;e<r;e++){const s=40+(o*r+e);n[s>>3]|=(1<<s%8)*(t[o]>>e&1)}return n})(r)},decompress:(o)=>{const r=(t=>{const o=t[0],r=t.slice(1,5).reverse().reduce((t,e)=>t<<8|e,0),n=new Uint32Array(r);for(let r=0;r<t[e];r++)for(let e=0;e<o;e++){const s=40+(r*o+e);n[r]|=(1<<e)*(t[s>>3]>>s%8&1)}return n})(o),n=[];for(let e=0;e<256;e++)n.push(t(e));let s=n[r[0]],c="";const l=[s];for(let t of r.slice(1))l.push(c=t<n[e]?n[t]:s+s[0]),n.push(s+c[0]),s=c;const f=[];for(let t of l.join(""))f.push(t.codePointAt(0));return new Uint8Array(f)}}})();

png.js

/**
 * Encode takes a string as input, encodes it as UTF8
 * then embeds it into a PNG which has builtin compression.
 * @param {string} input 
 * @returns {Promise<string>}
 */
async function encode(input) {
    const bytes = new TextEncoder("utf-8").encode(input);
    const canvas = document.createElement("canvas");
    canvas.width = Math.ceil(Math.sqrt(bytes.length / 3 + 2));
    canvas.height = canvas.width;
    const ctx = canvas.getContext('2d');
    const imgData = ctx.createImageData(canvas.width, canvas.height);
    for (let i = 0, j = 0; j < 4; i++)
        imgData.data[i] = i % 4 == 3 ? 255 : (bytes.length >> (8 * j++)) & 0xff;
    for (let i = 5, j = 0; i < 4 * canvas.width * canvas.height; i++)
        imgData.data[i] = i % 4 == 3 ? 255 : bytes[j++] || 0;
    ctx.putImageData(imgData, 0, 0);
    return canvas.toDataURL('image/png', 0);
}

/**
 * Reverse of encode.
 * @param {string} input 
 * @returns {Promise<string>}
 */
async function decode(input) {
    const image = new Image();
    image.src = input;
    await new Promise(r => image.onload = r);
    const canvas = document.createElement("canvas");
    canvas.width = image.width;
    canvas.height = image.height;
    const ctx = canvas.getContext('2d');
    ctx.drawImage(image, 0, 0);
    const imgData = ctx.getImageData(0, 0, image.width, image.height);
    let length = 0;
    for (let i = 0, j = 0; j < 4; i++)
        length |= i % 4 == 3 ? 0 : (imgData.data[i] << (8 * j++));
    const output = imgData.data
        .filter((_, i) => i > 4 && i % 4 != 3)
        .slice(0, length)
    return new TextDecoder("utf-8").decode(output);
}

png.min.js

(()=>{return{encode:async function(t){const e=new TextEncoder("utf-8").encode(t),a=document.createElement("canvas");a.width=Math.ceil(e.length/3+2),a.height=1;const n=a.getContext("2d"),c=n.createImageData(a.width,1);for(let t=0,a=0;a<4;t++)c.data[t]=t%4==3?255:e.length>>8*a++&255;for(let t=5,n=0;t<4*a.width;t++)c.data[t]=t%4==3?255:e[n++]||0;return n.putImageData(c,0,0),a.toDataURL("image/png",0)},decode:async function(t){const e=new Image;e.src=t,await new Promise(t=>e.onload=t);const a=document.createElement("canvas");a.width=e.width,a.height=1;const n=a.getContext("2d");n.drawImage(e,0,0);const c=n.getImageData(0,0,e.width,1);let o=0;for(let t=0,e=0;e<4;t++)o|=t%4==3?0:c.data[t]<<8*e++;const d=c.data.filter((t,e)=>e>4&&e%4!=3).slice(0,o);return new TextDecoder("utf-8").decode(d)}}})();