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Linking HTML checkbox with Javascript

How to link checkbox from HTML in java script? I set the checkbox in HMTL as follows:  <label><b>Response Needed ?</b></label> <input id="Check" type="checkbox" >

When I click the submit button, I need the value to be T (true) or F (false) if it is checked or not.

I usually use getElementById("")to link things with Javascirpt, but I can't get it to work!

EDIT: Here is my complete document so you can see how it works:

`

<!DOCTYPE HTML>
<html>
<head lang="en">
<meta charset="UTF-8"> 

 </head>

<body>

<form id="OTA">

    <label><b>IMEI:</b></label>
<input type="text" name="ID" id="IMEI" maxlength="15"> 

    <label><b>AT Command:</b></label>
    <input id="Command" type="text">

    <label><b>Response Needed ?</b></label>
    <input id="Check" type="checkbox" >


</form>
    <input type="submit" value="Submit" onclick="showInput();"><br />
    <p><span id='display'></span> </p> 

    <script language="JavaScript">
function showInput() {

    var message_entered = ">RSP=" + document.getElementById("Check").checked + ";ID=" +  document.getElementById("IMEI").value + ";" + document.getElementById("Command").value + "<";

    document.getElementById('display').innerHTML = message_entered;

}
    </script>

</body>

</html>

I need to change the values ​​of the T and F checkbox if they are set or not. Greetings

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3 answers

here are some javascript

 <form id="OTA">
    
        <label><b>IMEI:</b></label>
    <input type="text" name="ID" id="IMEI" maxlength="15"> 
    
        <label><b>AT Command:</b></label>
        <input id="Command" type="text">
    
        <label><b>Response Needed ?</b></label>
        <input id="Check" type="checkbox" >
    
    
    </form>
        <input type="submit" value="Submit" onclick="showInput();"><br />
        <p><span id='display'></span> </p> 
    
        <script language="JavaScript">
    function showInput() {
         var test=null;
    var obj=document.getElementById("Check").checked;
    obj?test='t':test='f';
      var message_entered = ">RSP=" +test+  document.getElementById("IMEI").value + ";" + document.getElementById("Command").value + "<";
        document.getElementById('display').innerHTML = message_entered;
    
    }
        </script>
Run code
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Well ... if you want to check if the checkbox is checked or not (True or False), you can use document.getElementById("Check").checked

if (document.getElementById("Check").checked) 
    console.log("checked");
else 
    console.log("not checked");
+1

In your submit button, call some javascript method, as shown below:

<form action="someAction" method="post"  onSubmit="javascript:validate()">
<input type="hidden" name="checkValue" id="checkValue" value='F'/> <!--Default value is F say -->
<submit></submit>
</form>

Now below is the validate function:

<script>
function validate(){
  if (document.getElementById("Check").checked){ 
     document.getElementById("checkValue").value = 'T'
  }else{ 
     document.getElementById("checkValue").value = 'F'
  }
}
</script>

There is only one drawback: you need to have a checkbox with a name different from the original name that you wanted, since this original name will go into a hidden field.

Hope this helps!

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Source: https://habr.com/ru/post/1621785/

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