Write full types and fix related bugs

Also fixes #4.

src/lib/structures/TimelineBaseMethods.js

@@ -0,0 +1,33 @@
+const constants = require("../constants")
+const {proxyImage, proxyExtendedOwner} = require("../utils/proxyurl")
+
+class TimelineBaseMethods {
+	constructor() {
+		/** @type {import("../types").GraphChildAll & {owner?: any}} */
+		this.data
+	}
+
+	getType() {
+		if (this.data.__typename === "GraphImage") {
+			if (this.data.owner) return constants.symbols.TYPE_IMAGE
+			else return constants.symbols.TYPE_GALLERY_IMAGE
+		} else if (this.data.__typename === "GraphVideo") {
+			if (this.data.owner) return constants.symbols.TYPE_VIDEO
+			else return constants.symbols.TYPE_GALLERY_VIDEO
+		} else if (this.data.__typename === "GraphSidecar") {
+			return constants.symbols.TYPE_GALLERY
+		} else {
+			throw new Error("Unknown shortcode __typename: "+this.data.__typename)
+		}
+	}
+
+	getDisplayUrlP() {
+		return proxyImage(this.data.display_url)
+	}
+
+	getAlt() {
+		return this.data.accessibility_caption || "No image description available."
+	}
+}
+
+module.exports = TimelineBaseMethods