DJCtrlEmu/preload.js

const electron = require("electron");

let volumeMeterLeft;
let volumeMeterRight;

function sendControl(name, value = 0x00) {
	electron.ipcRenderer.invoke("control", name, value);
}

electron.contextBridge.exposeInMainWorld("controller", {
	"load": function (deckIndex) {
		sendControl("deck" + String(deckIndex) + ".load");
	},
	"play_pause": function (deckIndex) {
		sendControl("deck" + String(deckIndex) + ".play_pause");
	},
	"sync": function (deckIndex) {
		sendControl("deck" + String(deckIndex) + ".sync");
	},
	"volume": function (deckIndex, value) {
		sendControl("deck" + String(deckIndex) + ".volume", value);
	},
	"eq": function (deckIndex, freq, value) {
		sendControl("deck" + String(deckIndex) + ".eq_" + freq, value);
	},
	"speed": function (deckIndex, value) {
		sendControl("deck" + String(deckIndex) + ".speed", value);
	},
	"pad": function (deckIndex, padIndex) {
		sendControl("deck" + String(deckIndex) + ".pad" + String(padIndex));
	},
	"crossfade": function (value) {
		sendControl("master.crossfade", value);
	}
});

electron.ipcRenderer.on("signal", function (event, name, value = 0x00) {
	switch (name) {
		case "master.volume.left":
			volumeMeterLeft.style.height = String(Math.round((value / 80) * 100)) + "%";
			break;
		case "master.volume.right":
			volumeMeterRight.style.height = String(Math.round((value / 80) * 100)) + "%";
			break;
		default:
			break;
	}
});

electron.ipcRenderer.invoke("load-driver", "linux-rawmidi");
electron.ipcRenderer.invoke("load-mappings", "numark-mixtrackplatinum");

(async function () {
	var devices = await electron.ipcRenderer.invoke("list-devices");

	if (devices.length > 0) {
		electron.ipcRenderer.invoke("open-device", devices[0]);
	}
})();

window.onload = function (event) {
	volumeMeterLeft = document.querySelector("#volume-meter-left");
	volumeMeterRight = document.querySelector("#volume-meter-right");
};