getValue

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Get Text Input Field Value in JavaScript</title>
</head>
<body>
    <input type="text" placeholder="Type something..." id="myInput">
    <button type="button" onclick="getInputValue();">Get Value</button>

    <script>
        function getInputValue(){
            // Selecting the input element and get its value
            var inputVal = document.getElementById("myInput").value;

            // Displaying the value
            alert(inputVal);
        }
    </script>
</body>
</html>