you can add the "check all" in the header directly in the handsontable colHeaders and to apply UniformJS you need to use the callback afterRender like this
$("#example1").handsontable({
data: getCarData(),
startRows: 7,
startCols: 4,
colHeaders: ["Car", "Year", "<input type='checkbox' class='checkall' />"],//checkall inside colHeaders
colWidths: [120, 50, 60],
columnSorting: true,
columns: [
{
data: "car"
},
{
data: "year",
type: 'numeric'
},
{
data: "available",
type: "checkbox"
}
],
//afterRender so all the "available" checkbox use UniformJS
afterRender:function(){
$('input').uniform();
//click handler for .checkall
$('.checkall').on('click', function () {
//get all .htCheckboxRendererInput and change the property checked
$(this).closest('table').find('input.htCheckboxRendererInput').prop("checked",this.checked);
$.uniform.update();//update UniformJS
});
}
});