Apex Coding on Mass Delete Records Using List Button in Java Scripts.....

{!REQUIRESCRIPT("/soap/ajax/9.0/connection.js")}

var records = {!GETRECORDIDS( $ObjectType.Event )};
var taskRecords = {!GETRECORDIDS( $ObjectType.Task)};
records = records.concat(taskRecords);


if (records[0] == null) {
alert("Please select at least one record.") }
else {

var errors = [];
var result = sforce.connection.deleteIds(records);
if (result &result.length)
{
alert(result);
alert(result);
var numFailed = 0;
var numSucceeded = 0;
for (var i = 0; i < result.length; i++){
alert(i);
var res = result[i];
if (res && res.success == 'true'){
numSucceeded++;
} else {
var es = res.getArray("errors");
if (es.length > 0) {
errors.push(es[0].message);
}
numFailed++;
}
}
if (numFailed > 0){
alert("Failed: " + numFailed + "\nSucceeded: " + numSucceeded + " \n Due to: " + errors.join("\n"));
} else {
alert("Number of records deleted: " + numSucceeded);
}
}
window.location.reload();
}