Javascript checkbox onChange

user_511488 0
Viewed 720650

I have a checkbox in a form and I'd like it to work according to following scenario:

  • if someone checks it, the value of a textfield (totalCost) should be set to 10.
  • then, if I go back and uncheck it, a function calculate() sets the value of totalCost according to other parameters in the form.

So basically, I need the part where, when I check the checkbox I do one thing and when I uncheck it, I do another.

checkbox javascript
10 Answers

Pure javascript:

const checkbox = document.getElementById('myCheckbox')

checkbox.addEventListener('change', (event) => {
  if (event.currentTarget.checked) {
    alert('checked');
  } else {
    alert('not checked');
  }
})
My Checkbox: <input id="myCheckbox" type="checkbox" />

user_8262900

HTML:

<input type="checkbox" onchange="handleChange(event)">

JS:

function handleChange(e) {
     const {checked} = e.target;
}
user_79642170

I know this seems like noob answer but I'm putting it here so that it can help others in the future.

Suppose you are building a table with a foreach loop. And at the same time adding checkboxes at the end.

<!-- Begin Loop-->
<tr>
 <td><?=$criteria?></td>
 <td><?=$indicator?></td>
 <td><?=$target?></td>
 <td>
   <div class="form-check">
    <input type="checkbox" class="form-check-input" name="active" value="<?=$id?>" <?=$status?'checked':''?>> 
<!-- mark as 'checked' if checkbox was selected on a previous save -->
   </div>
 </td>
</tr>
<!-- End of Loop -->

You place a button below the table with a hidden input:

<form method="post" action="/goalobj-review" id="goalobj">

 <!-- we retrieve saved checkboxes & concatenate them into a string separated by commas.i.e. $saved_data = "1,2,3"; -->

 <input type="hidden" name="result" id="selected" value="<?= $saved_data ?>>
 <button type="submit" class="btn btn-info" form="goalobj">Submit Changes</button>
</form>

You can write your script like so:

<script type="text/javascript">
    var checkboxes = document.getElementsByClassName('form-check-input');
    var i;
    var tid = setInterval(function () {
        if (document.readyState !== "complete") {
            return;
        }
        clearInterval(tid);
    for(i=0;i<checkboxes.length;i++){
        checkboxes[i].addEventListener('click',checkBoxValue);
    }
    },100);

    function checkBoxValue(event) {
        var selected = document.querySelector("input[id=selected]");
        var result = 0;
        if(this.checked) {

            if(selected.value.length > 0) {
                result = selected.value + "," + this.value;
                document.querySelector("input[id=selected]").value = result;
            } else {
                result = this.value;
                document.querySelector("input[id=selected]").value = result;
            }
        }
        if(! this.checked) { 

// trigger if unchecked. if checkbox is marked as 'checked' from a previous saved is deselected, this will also remove its corresponding value from our hidden input.

            var compact = selected.value.split(","); // split string into array
            var index = compact.indexOf(this.value); // return index of our selected checkbox
            compact.splice(index,1); // removes 1 item at specified index
            var newValue = compact.join(",") // returns a new string
            document.querySelector("input[id=selected]").value = newValue;
        }

    }
</script>

The ids of your checkboxes will be submitted as a string "1,2" within the result variable. You can then break it up at the controller level however you want.

user_61310330

try

totalCost.value = checkbox.checked ? 10 : calculate();


function change(checkbox) {
  totalCost.value = checkbox.checked ? 10 : calculate();
}

function calculate() {
  return other.value*2;
}
input { display: block}
Checkbox: <input type="checkbox" onclick="change(this)"/>
Total cost: <input id="totalCost" type="number" value=5 />
Other: <input id="other" type="number" value=7 />

user_8600990
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