How to unpivot table in Google Sheets?

Unpivot

function unpivot() {
  const ss = SpreadsheetApp.getActive();
  const sh = ss.getSheetByName("Sheet0");
  const osh = ss.getSheetByName("Sheet1");
  const [h, ...vs] = sh.getRange(1, 1, sh.getLastRow(), sh.getLastColumn()).getValues();
  let n = 0;
  let obj = { pA: [] }
  vs.forEach((r, i) => {
    if (!obj.hasOwnProperty(r[0])) {
      obj[r[0]] = { sA: [] };
      obj.pA.push(r[0]);
    } //collect the first column as properties
    r.forEach((c, j) => {
      if (j > 0) {
        if (!obj[r[0]].hasOwnProperty(h[j])) {
          obj[r[0]][h[j]] = c;
          obj[r[0]].sA.push(h[j])
        } //collecting the first row as properties and assigning the value to each subproperty
      }
    });
  });
  let oA = [];
  obj.pA.forEach(p => {
    obj[p].sA.forEach(s => oA.push([p,s,obj[p][s]]));
  });//separating them into a two dimensional array
  //Logger.log(JSON.stringify(oA));
  oA.sort((a,b) => new Date(a[1]).valueOf() - new Date(b[1]).valueOf());//sorting by date
  osh.clearContents();
  osh.getRange(1,1,oA.length,oA[0].length).setValues(oA);//displaying
}

Sheet0:

Sheet1: