eslint: Fix @typescript-eslint/prefer-string-starts-ends-with.

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

web/src/browser_history.ts

@@ -107,7 +107,7 @@ export function return_to_web_public_hash(): void {
 export function get_full_url(hash: string): string {
     const location = window.location;
 
-    if (hash.charAt(0) !== "#" && hash !== "") {
+    if (!hash.startsWith("#") && hash !== "") {
         hash = "#" + hash;
     }
 
@@ -115,7 +115,7 @@ export function get_full_url(hash: string): string {
     let pathname = location.pathname;
     if (pathname === undefined) {
         pathname = "/";
-    } else if (pathname === "" || pathname.charAt(0) !== "/") {
+    } else if (pathname === "" || !pathname.startsWith("/")) {
         pathname = "/" + pathname;
     }
 

web/src/channel.ts

@@ -210,7 +210,7 @@ export function patch(
 }
 
 export function xhr_error_message(message: string, xhr: JQuery.jqXHR<unknown>): string {
-    if (xhr.status.toString().charAt(0) === "4" && xhr.responseJSON?.msg) {
+    if (xhr.status >= 400 && xhr.status < 500 && xhr.responseJSON?.msg) {
         // Only display the error response for 4XX, where we've crafted
         // a nice response.
         const server_response_html = _.escape(xhr.responseJSON.msg);

web/src/hash_util.ts

@@ -11,7 +11,7 @@ type Operator = {operator: string; operand: string; negated?: boolean};
 
 export function build_reload_url(): string {
     let hash = window.location.hash;
-    if (hash.length !== 0 && hash[0] === "#") {
+    if (hash.length !== 0 && hash.startsWith("#")) {
         hash = hash.slice(1);
     }
     return "+oldhash=" + encodeURIComponent(hash);
@@ -177,7 +177,7 @@ export function parse_narrow(hash: string): Operator[] | undefined {
         }
 
         let negated = false;
-        if (operator[0] === "-") {
+        if (operator.startsWith("-")) {
             negated = true;
             operator = operator.slice(1);
         }