javascript (app script) to provide live validation on length of sms message within a given cell

smsLengthValidator.js

function onEdit({source, range}) {

    const {
        columnStart,
        rowStart
    } = range

    const nextCellR1C1Notation = `R${rowStart}C${columnStart + 1}`

    if (columnStart == 3) {

        const adjacentCell = source.getActiveSheet().getRange(nextCellR1C1Notation)

        const cellCharacterLength = range.getValue().toString().length

        if (cellCharacterLength > 0) {
            
            if (cellCharacterLength <= 50) {
                adjacentCell.setValue("A bit short");
                adjacentCell.setBackground("lightblue")
            }
            
            if (cellCharacterLength > 50 && cellCharacterLength <= 100) {
                adjacentCell.setValue("A decent length");
                adjacentCell.setBackground("orange")

            }
            
             if (cellCharacterLength > 100 && cellCharacterLength <= 150) {
                adjacentCell.setValue("A good length");
                adjacentCell.setBackground("lightgreen")
            }

            if (cellCharacterLength > 150) {
                adjacentCell.setValue("Too Long")
                adjacentCell.setBackground("#ffcccb")
            }

        } else {
            adjacentCell.setValue("");
            adjacentCell.setBackground("white")
        }

    }

}