Drop down to hide rows based on a dropdown - google-apps-script

Question

In Google Sheets I want to hide rows 5 to 31 when my drop down in R4 says BLS, and show those cells if R4 is blank or says ALS.
Here is my most recent attempt:
function onEdit(e) {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sh = ss.getSheetByName("Shee1");
var rg = sh.getDataRange();
var vA = rg.getValues();
var R4 = sh.getRange("R4").getValue();
for (var i = 0; i < vA.length; i++) {
var row = i + 1;
switch (R4) {
case "BLS":
if (row >= 5 && row <= 31) {
sh.hideRows(row);
}
break;
case "ALS":
if (row >= 4 && row <= 32) {
sh.showRows(row);
}
break;
default:
}
}
}
I have also tried this, which points to 2 different macros that I recorded but it makes the screen go crazy and jumps around whenever something else is edited:
function onEdit(){
if(SpreadsheetApp.getActiveSheet().getRange('R4').getValue() == "BLS") BLS(); // Launches the script
if(SpreadsheetApp.getActiveSheet().getRange('R4').getValue() == "ALS") ALS(); // Launches the script
}

Answer 1

function onEdit(e) {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var s = ss.getSheetByName("Sheet1"); // Enter sheet name
var row = s.getRange('R:R').getValues();
// Enter column letter that has the text "hide" and "unhide"
s.showRows(1, s.getMaxRows());
for(var i=0; i< row.length; i++){ if(row[i] == 'hide') { s.hideRows(i+1, 27); }
else if(row[i] == 'unhide'){ s.unhideRow(ss.getDataRange()); }
}
}