How to get the selected radio button value using js

all of you can test this example and easy to understand.

        Name:   <input type="text" id="text" class ="input">
                <input type="text" id="text1" class ="input">
        Gender: <input type="radio" id="m" class="Rm"  name="Rmale" value="Male">
                <input type="radio" id="f" class="Rm" name="Rfemale" value="Female">
        Course: <input type="checkbox" id="math" class="cm" name="Cmath" value="Math">
                <input type="checkbox" id="physic" class="cm" name="Cphysic" value="Physic">
                <input type="checkbox" id="eng" class="cm"  name="Ceng" value="English">
        <button type="button" id="b1">show</button>

// javascript

    <script>
        function getData(input){
            return document.getElementById(input).value;
        }
        function dataByClassName(st){
            var value=document.getElementsByClassName(st)
            for(var i=0;i < value.length;i++){
                if(value[i].checked){
                    return value[i].value;
                }
            }
        }
        document.getElementById("b1").onclick = function ()
        {
            var st={
                name : getData("text")+getData("text1"),
                gender : dataByClassName("Rm"),
                course : dataByClassName("cm")
            };
            alert(st.name+" "+st.gender+" "+st.course);
        };

    </script>

Try this, I hope this one will work

function loadRadioButton(objectName, selectedValue) {

    var radioButtons = document.getElementsByName(objectName);

    if (radioButtons != null) {
        for (var radioCount = 0; radioCount < radioButtons.length; radioCount++) {
            if (radioButtons[radioCount].value == selectedValue) {
                radioButtons[radioCount].checked = true;
            }
        }
    }
}

Use:

document.querySelector('#elementId:checked').value;

This will return the value of the selected radio button.

Please try this:

this.template.querySelector('input[name = "gender"]:checked').value;