global: Specialize jQuery .val() for elements with known value types.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

web/src/global.d.ts

@@ -22,7 +22,21 @@ declare namespace JQueryValidation {
 }
 
 // eslint-disable-next-line @typescript-eslint/consistent-type-definitions
-interface JQuery {
+interface JQuery<TElement = HTMLElement> {
+    // Specialize .val() for elements with known value types.
+    // https://github.com/DefinitelyTyped/DefinitelyTyped/pull/66801
+    val():
+        | (TElement extends HTMLSelectElement & {type: "select-one"}
+              ? string
+              : TElement extends HTMLSelectElement & {type: "select-multiple"}
+              ? string[]
+              : TElement extends HTMLSelectElement
+              ? string | string[]
+              : TElement extends {value: string | number}
+              ? TElement["value"]
+              : string | number | string[])
+        | undefined;
+
     expectOne(): this;
     get_offset_to_window(): DOMRect;
     tab(action?: string): this; // From web/third/bootstrap

web/src/rtl.ts

@@ -1,5 +1,4 @@
 import _ from "lodash";
-import assert from "minimalistic-assert";
 
 // How to determine the direction of a paragraph (P1-P3): https://www.unicode.org/reports/tr9/tr9-35.html#The_Paragraph_Level
 // Embedding level: https://www.unicode.org/reports/tr9/tr9-35.html#BD2
@@ -142,8 +141,7 @@ export function get_direction(str: string): "ltr" | "rtl" {
 
 export function set_rtl_class_for_textarea($textarea: JQuery<HTMLTextAreaElement>): void {
     // Set the rtl class if the text has an rtl direction, remove it otherwise
-    let text = $textarea.val();
-    assert(typeof text === "string", "Passed HTML element must be a textarea.");
+    let text = $textarea.val()!;
     if (text.startsWith("```quote")) {
         text = text.slice(8);
     }