Ultra-compact lzstring decompress implementation.

lzstring-tiny.js

function decompress(buf) {
  const fromCharCode = String.fromCharCode
  const invalid = new Error("invalid")

  let idx = 0, u16 = 0, bit = 0
  const uint = bits => {
    let res = 0
    for (let i = 0; i < bits; i++) {
      if (bit == 0) {
        if (idx >= buf.length) {
          throw invalid // unexpected end of stream
        }
        bit = 1<<(16-1)
        u16 = buf.charCodeAt(idx++)
      }
      if (u16 & bit) {
        res |= 1 << i
      }
      bit >>= 1
    }
    return res
  }

  let last, dict = [], res = ""
  for (;;) {
    const dictSize = dict.length
    const bits = 32-Math.clz32(3+dictSize)
    let op = uint(bits)
    if (op == 2) {
      return res
    }
    let chunk
    if (op > 2) {
      op -= 3
      if (!last || op > dictSize) {
        throw invalid // first packet must be a literal || dictionary index out of range
      }
      if (op < dictSize) {
        chunk = dict[op]
      } else {
        chunk = last + last.charAt(0)
      }
    } else {
      chunk = fromCharCode(uint(op?16:8))
      dict.push(chunk)
    }
    if (last) {
      dict.push(last + chunk.charAt(0))
    }
    last = chunk
    res += chunk
  }
}

lzstring-tiny.min.js

function decompress(r){let t=String.fromCharCode,e=Error("invalid"),h=0,o=0,f=0,i=t=>{let i=0;for(let l=0;l<t;l++){if(0==f){if(h>=r.length)throw e;f=32768,o=r.charCodeAt(h++)}o&f&&(i|=1<<l),f>>=1}return i},l,n=[],a="";for(;;){let r,h=n.length,o=i(32-Math.clz32(3+h));if(2==o)return a;if(o>2){if(o-=3,!l||o>h)throw e;r=o<h?n[o]:l+l.charAt(0)}else r=t(i(o?16:8)),n.push(r);l&&n.push(l+r.charAt(0)),l=r,a+=r}}