Select All option for Lookup fields

Scenario:
Lookup with multi-select option is available as a field for any list we create. And it has Add and Remove buttons to make selection but misses Add All and Remove All.

Solution:
This is a small workaround. Add a check-box column to the list as shown below.
Now you need to find some control guids. You can use my favorite X-ray machine Internet Explorer Developer Toolbar.

Steps:
1. Enter into edit mode of the NewForm.aspx ( type javascript:MSOLayout_ToggleLayoutMode(); in the IE Address bar and hit enter )

2. Add a Content Editor Webpart at the bottom ( make sure it is the last webpart )

3. Paste the script given below ( make sure to change the control ids )


Code:

 <script type="text/javascript">

        function button_click(controlid,AddButtonControlId) 
        {
            var myselect = document.getElementById(controlid)
            
            for (var i = 0; i < myselect.options.length; i++) 
            {
                myselect.options[i].selected = true ; 
            }
                
                 for (var i = 0; i < myselect.options.length; i++) 
                 {
                    if (myselect.options[i].selected == true)
                 {
 GipAddSelectedItems(AddButtonControlId);

                   }
                }
        }

function SelectAll()
{

// passed paramters
// 1. select control ( must be in quotes ) - ends in SelectCandidate
// 2. Picker control id ( must not have quotes ) - ends in MultiLookupPicker_m
button_click("ctl00_m_g_dbc86119_02b0_465b_8e56_2764e7284a1d_ctl00_ctl04_ctl01_ctl00_ctl00_ctl04_ctl00_ctl00_SelectCandidate",ctl00_m_g_dbc86119_02b0_465b_8e56_2764e7284a1d_ctl00_ctl04_ctl01_ctl00_ctl00_ctl04_ctl00_ctl00_MultiLookupPicker_m) ;
}

// passed paramters
// 1. check box control ( must be in quotes ) 

    var checkit = document.getElementById("ctl00_m_g_dbc86119_02b0_465b_8e56_2764e7284a1d_ctl00_ctl04_ctl03_ctl00_ctl00_ctl04_ctl00_ctl00");
        checkit.onclick = SelectAll;

</script>