برای انجام این کار یکی از کدهای زیر را در یک Script editor وارد کنید.

<input type="button" id="btnDeleteItems" value="Click Here"/>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>

<script>
$(document).ready(function(){
$("#btnDeleteItems").click(function(){
DeleteAllItems();
});
});

function DeleteAllItems(){
var ctx = SP.ClientContext.get_current(),
list = ctx.get_web().get_lists().getByTitle('Ideas'),
query = new SP.CamlQuery(),
items = list.getItems(query);
ctx.load(items, "Include(Id)");
ctx.executeQueryAsync(function () {
var enumerator = items.getEnumerator(),
itemArray = [];
while (enumerator.moveNext()) {
itemArray.push(enumerator.get_current());
}

for (var s in itemArray) {
itemArray[s].deleteObject();
}
ctx.executeQueryAsync();
});
}
</script>

<input type="button" id="btnSubmit" value="Delete All Items" /><br/>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
<script>
$(function () {
bindButtonClick();
});
function bindButtonClick() {
$("#btnSubmit").on("click", function () {
deleteAllItemsFromList();
});
}

var clientContext;
var website;
var oList;
var cnt = 0;

function deleteAllItemsFromList() {
clientContext = SP.ClientContext.get_current();
website = clientContext.get_web();
oList = website.get_lists().getByTitle('SourceList');

var camlQuery = new SP.CamlQuery();
camlQuery.set_viewXml('<View><RowLimit>100</RowLimit></View>');
this.collListItem = oList.getItems(camlQuery);

clientContext.load(website);
clientContext.load(collListItem, 'Include(Id)');
clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}

function onQuerySucceeded(sender, args) {
var listItemInfo = ";
var listItemEnumerator = collListItem.getEnumerator();
while (listItemEnumerator.moveNext()) {
var oListItem = listItemEnumerator.get_current();
var ID = oListItem.get_id();
var oListItemDel = oList.getItemById(ID);
oListItemDel.deleteObject();
clientContext.executeQueryAsync(Function.createDelegate(this, this.onDeleteSucceeded), Function.createDelegate(this, this.onDeleteFailed));
}
}

function onQueryFailed(sender, args) {
alert('Failed');
}

function onDeleteFailed(sender, args) {
alert('Failed');
}

function onDeleteSucceeded(sender, args) {
cnt = cnt + 1;
alert('Delete success : ' + cnt);
}
</script>

حذف همه ی موارد یک لیست با استفاده از JavaScript object model (jsom)