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How do I determine if a checkbox is checked?

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我在风中等你
我在风中等你 2020-11-27 05:23

For some reason, my form does not want to get the value of a checkbox... I am not sure if it is my coding or not, but when I try and alert() the value, I get

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  • 暖寄归人
    2020-11-27 05:50

    Place the var lfckv inside the function. When that line is executed, the body isn't parsed yet and the element "lifecheck" doesn't exist. This works perfectly fine:

    function exefunction() {
  var lfckv = document.getElementById("lifecheck").checked;
  alert(lfckv);
}
    <label><input id="lifecheck" type="checkbox" >Lives</label>
<button onclick="exefunction()">Check value</button>

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  • 说谎
    2020-11-27 05:55

    Following will return true when checkbox is checked and false when not.

    $(this).is(":checked")

    Replace $(this) with the variable you want to check.

    And used in a condition:

    if ($(this).is(":checked")) {
  // do something
}
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  • 挽巷
    2020-11-27 05:57 
    <!DOCTYPE html>
<html>
<body>
    <input type="checkbox" id="isSelected"/>
    <div id="myDiv" style="display:none">Is Checked</div>
</body>

    <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
    <script>
        $('#isSelected').click(function() {
            $("#myDiv").toggle(this.checked);
        });
    </script>
</html>
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  • 面向向阳花
    2020-11-27 05:58

    The line where you define lfckv is run whenever the browser finds it. When you put it into the head of your document, the browser tries to find lifecheck id before the lifecheck element is created. You must add your script below the lifecheck input in order for your code to work.

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  • 不思量自难忘°
    2020-11-27 06:01

    try learning jQuery it's a great place to start with javascript and it really simplifies your code and help separate your js from your html. include the js file from google's CDN (https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js)

    then in your script tag (still in the <head>) use:

    $(function() {//code inside this function will run when the document is ready
    alert($('#lifecheck').is(':checked'));

    $('#lifecheck').change(function() {//do something when the user clicks the box
        alert(this.checked);
    });
});
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  • 野的像风
    2020-11-27 06:05

    You are trying to read the value of your checkbox before it is loaded. The script runs before the checkbox exists. You need to call your script when the page loads:

    <body onload="dosomething()">

    Example:

    http://jsfiddle.net/jtbowden/6dx6A/

    You are also missing a semi-colon after your first assignment.

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