<p class="rowBox">
        <label>Text box</label>
        <input type="text"
               id="myText"
               value="text here" /> <--- want to insert local storage to replace "text here"
    </p>

javascript file containing this:

        function getFirstRow() {
            let firstRow = Number(JSON.parse((<HTMLInputElement>document.getElementById('myText')).value)) + 3;
            if (isNaN(firstRow) || firstRow > rowCount || firstRow < 4 || firstRow == undefined || firstRow == null || firstRow > 		rowCount || !(typeof firstRow === 'number' && (firstRow % 1) === 0)) {
                return '3:';
            } else {
                localStorage.startRow = JSON.stringify(firstRow);
                return firstRow + ':';
            }
        }