lord-max

function checksum_12_words_min(data) {
  let binstr = (s,l =8) => s.toString(2).padStart(l,'0') // convert to binary `0011...` string
  let tohex = (bytes) => bytes.map( x => x.toString(16).padStart(2,0) ).join('')                                  
  let bytes = data.map( x => binstr(x - 1, 11)).join('').match(/.{1,8}/g).map( x => parseInt(x, 2))	
  bytes.pop(); console.log("Entropy is :",tohex(bytes))  
  window.crypto.subtle.digest("SHA-256", new Uint8Array(bytes).buffer).then( x => {
    let hash = new Uint8Array(x)
    let cs = binstr(hash[0]).match(/.{1,4}/g)[0]
    let bits = [binstr(bytes[15]),cs].join('')
    console.log("Your 12th word index is: " + (1+parseInt(bits.substr(1),2)))

lord-max

// We expect array of 12 words as human readable indexes (1-2048)
function checksum_12_words(data) {
  if (data.length != 12) return console.log("ERROR: Need 12 words numbers as input")
  
  let binstr = (s,l =8) => s.toString(2).padStart(l,'0') // convert to binary `0011...` string
  let tohex = (bytes) => bytes.map( x => x.toString(16).padStart(2,0) ).join('')
                                   
  let bytes = data.map( x => binstr(x - 1, 11)) // convert to 0-index, then to binary `0011...` 
                .join('').match(/.{1,8}/g) 	// split 8 bits	
                .map( x => parseInt(x, 2))	// convert to UInt8