Selecting/deselecting checkboxes

Discussion in 'Javascript' started by Jez, Jul 17, 2003.

  1. Jez

    Jez Guest


    I have created the following functions to select and deselect
    checkboxes in a form ...

    function check(checkbox) {
    for (i = 0; i < checkbox.length; i++) {
    checkbox.checked = true;
    return "Select all";

    function uncheck(checkbox) {
    for (i = 0; i < checkbox.length; i++) {
    checkbox.checked = false;
    return "Select none";

    The form itself looks like this ...

    <form name="form" action="delete.php" method="post">
    <input type="checkbox" name="id" value="1" />Option 1<br />
    <input type="checkbox" name="id" value="2" />Option 2<br />
    <input type="checkbox" name="id" value="3" />Option 3<br />
    <input type="button" value="Select all"
    onClick="this.value=check(" />
    <input type="button" value="Select none"
    onClick="this.value=uncheck(" />
    <input type="submit" name="submit" value="Delete selected" />

    This all seems to work very well (although constructive critisism
    would be welcome), however I actually need to name the input 'id[]'
    because I'm generating an array of values. Unfortunately the funtions
    don't seem to like '[]'. Is there anything I can do?

    Thank you in advance for your help. It's greatly appreciated!

    Jez, Jul 17, 2003
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  2. Feeding an array of checkboxes into a php script?

    <input type="checkbox" name="id[]" id="id" value="1">
    <input type="checkbox" name="id[]" id="id" value="2">
    <input type="checkbox" name="id[]" id="id" value="3">

    or try:

    <input type="button" value="Select all"
    onClick="this.value=check(this.form.elements['id[]'])" />
    <input type="button" value="Select none"
    onClick="this.value=uncheck(this.form.elements['id[]'])" />
    Richard Hockey, Jul 17, 2003
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  3. Jez

    Jez Hailwood Guest

    Thanks, that's excellent!

    My function now works perfectly unless there's only one checkbox, in
    which case it doesn't work at all.

    Any ideas?

    Jez Hailwood, Jul 17, 2003
  4. A single checkbox doesn't have a length property, so you can't loop through
    using id.length, you have to specifically check the id

    An example I pulled from a page which dynamically generates a group of

    // check for single checkbox by seeing if an array has been created
    var cblength=document.forms['inbox'].elements['del'].length;
    if(typeof cblength=="undefined")
    if(document.forms['inbox'].elements['del'].checked==true) count++;
    if(document.forms['inbox'].elements['del'].checked) count++;

    Assuming you are using php

    <input type="checkbox" name="bob" value="3">

    and in the php

    // checkbox 'bob' has been checked in the form
    // variable $bob will be set to the value of checkbox 'bob', in this case
    // checkbox 'bob' has not been checked, set a default value
    Richard Hockey, Jul 18, 2003
  5. Jez

    Jez Guest

    Problem now solved with a much simpler solution ...

    function selectAll(state) {
    for (i = 0; i < document.form.elements.length; i++) {
    var checkbox = document.form.elements;
    checkbox.checked = state;

    <input type="button" value="Select all" onClick="selectAll(true);" />
    <input type="button" value="Clear all" onClick="selectAll(false);" />

    Jez, Jul 18, 2003
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