# Asynchronous Validation (JavaScript Scheduler) | DayPilot Pro for JavaScript Demo

> Event resizing and moving is validated on drop using an asynchronous HTTP call. Read more about [event moving validation](https://doc.daypilot.org/scheduler/event-moving-validation/) and [event resizing validation](https://doc.daypilot.org/scheduler/event-resizing-validation/).

## Links

- Canonical HTML: /demo/scheduler/asyncvalidation.html
- Source HTML folder: /demo/scheduler/
- Catalog root: /demo/
- Catalog: /demo/llms.txt

## Source

### Inline demo script 1

```javascript
const dp = new DayPilot.Scheduler("dp", {
            startDate: "2026-01-01",
            days: 365,
            scale: "Day",
            timeHeaders: [
                {groupBy: "Month", format: "MMMM yyyy"},
                {groupBy: "Cell", format: "d"}
            ],
            treeEnabled: true,
            resources: [
                {
                    name: "Locations", id: "G1", expanded: true, children: [
                        {name: "Room 1", id: "A"},
                        {name: "Room 2", id: "B"},
                        {name: "Room 3", id: "C"},
                        {name: "Room 4", id: "D"}
                    ]
                },
                {
                    name: "People", id: "G2", expanded: true, children: [
                        {name: "Person 1", id: "E"},
                        {name: "Person 2", id: "F"},
                        {name: "Person 3", id: "G"},
                        {name: "Person 4", id: "H"}
                    ]
                },
                {
                    name: "Tools", id: "G3", expanded: true, children: [
                        {name: "Tool 1", id: "I"},
                        {name: "Tool 2", id: "J"},
                        {name: "Tool 3", id: "K"},
                        {name: "Tool 4", id: "L"}
                    ]
                },
            ],
            onEventMove: async args => {
                args.async = true;
                dp.message("Checking....");
                const {data} = await DayPilot.Http.get("asyncvalidation.txt");

                if (data.error) {
                    dp.message(data.message);
                    args.preventDefault();
                }
                args.loaded();
            },
            onEventMoved: args => {
                dp.message("Moved: " + args.e.text());
            },
            blockOnCallBack: false,
            onEventResize: async args => {
                args.async = true;
                dp.message("Checking....");
                const {data} = await DayPilot.Http.get("asyncvalidation.txt");

                if (data.error) {
                    dp.message(data.message);
                    args.preventDefault();
                }
                args.loaded();
            },
            onEventResized: args => {
                dp.message("Resized: " + args.e.text());
            },
            onTimeRangeSelected: async args => {
                const modal = await DayPilot.Modal.prompt("New event name:", "Event");
                dp.clearSelection();
                if (modal.canceled) {
                    return;
                }
                dp.events.add({
                    start: args.start,
                    end: args.end,
                    id: DayPilot.guid(),
                    resource: args.resource,
                    text: modal.result
                });
                dp.message("Created");
            },
            height: 300
        });
        dp.init();
        dp.scrollTo("2026-03-25");

        const app = {
            init() {
                this.loadEventData();
                this.addEventHandlers();
            },
            loadEventData() {
                // generate and load events
                const events = [];

                for (let i = 0; i < 15; i++) {
                    const duration = Math.floor(Math.random() * 6) + 1; // 1 to 6
                    const durationDays = Math.floor(Math.random() * 6 + 2); // 2 to 7
                    const start = Math.floor(Math.random() * 6) + 2; // 2 to 7

                    const resId = String.fromCharCode(65 + i);

                    const event = {
                        start: new DayPilot.Date("2026-03-25T00:00:00").addDays(start),
                        end: new DayPilot.Date("2026-03-25T12:00:00").addDays(start).addDays(durationDays).addHours(duration),
                        id: DayPilot.guid(),
                        resource: resId,
                        text: `Event ${i + 1}`
                    };

                    events.push(event);
                }
                dp.update({events});
            },
            addEventHandlers() {
                document.querySelector("#blockoncallback").addEventListener("change", function() {
                    const checked = this.checked;
                    dp.blockOnCallBack = checked;
                });
            }
        };
        app.init();
```