SvelteKit File Upload Example

+page.server.ts

import {writeFileSync, existsSync, mkdirSync} from "fs"

// make sure tmp directory exists and create it if it doesn't
function checkTmp() {
    if (!existsSync("static/tmp")) {
        mkdirSync("static/tmp")
    }
}

export const actions = {

    /**
     * Handles upload and saves file in tmp folder.
     * Returns error + code if something happens, otherwise returns
     * filename to pass onto the next stage.
     */
    upload: async ({request}: any) => {

        const formData = Object.fromEntries(await request.formData());

        // split filename into name + extension
        let name = formData.video.name;
        name = name.split(".")

        // get buffer to video
        let video = await formData.video.arrayBuffer()

        checkTmp()

        let error = false
        let error_msg = null

        try {
            writeFileSync(`static/tmp/${name[0]}.${name[1]}`, Buffer.from(video))
        } catch (e) {
            error = true
            error_msg = e
        }

        if (error) {
            return {
                code: -1,
                msg: error_msg.code
            }
        } else {
            return {
                code: 200,
                filename: `${name[0]}.${name[1]}`
            }
        }
    }
}

A basic example of how to do file upload. Waits for form data that sends an input file with the name video, writes it to directory called tmp.

Adjust as needed.