diff --git a/.eslintrc.json b/.eslintrc.json
index 4b4fdb2af9..e9f1148132 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -145,6 +145,7 @@
                 "no-duplicate-imports": "off",
                 "no-unused-vars": "off",
                 "no-useless-constructor": "off",
+                "no-use-before-define": "off",
 
                 "@typescript-eslint/array-type": "error",
                 "@typescript-eslint/await-thenable": "error",
diff --git a/static/js/blueslip.js b/static/js/blueslip.ts
similarity index 83%
rename from static/js/blueslip.js
rename to static/js/blueslip.ts
index b3ef413309..bfc2b1fce1 100644
--- a/static/js/blueslip.js
+++ b/static/js/blueslip.ts
@@ -16,12 +16,12 @@ if (Error.stackTraceLimit !== undefined) {
     Error.stackTraceLimit = 100000;
 }
 
-function pad(num, width) {
+function pad(num: number, width: number): string {
     return num.toString().padStart(width, "0");
 }
 
-function make_logger_func(name) {
-    return function Logger_func(...args) {
+function make_logger_func(name: "debug" | "log" | "info" | "warn" | "error") {
+    return function Logger_func(this: Logger, ...args: unknown[]) {
         const now = new Date();
         const date_str =
             now.getUTCFullYear() +
@@ -62,27 +62,26 @@ class Logger {
     warn = make_logger_func("warn");
     error = make_logger_func("error");
 
-    _memory_log = [];
-
-    get_log() {
+    _memory_log: string[] = [];
+    get_log(): string[] {
         return this._memory_log;
     }
 }
 
 const logger = new Logger();
 
-export function get_log() {
+export function get_log(): string[] {
     return logger.get_log();
 }
 
-const reported_errors = new Set();
-const last_report_attempt = new Map();
+const reported_errors = new Set<string>();
+const last_report_attempt = new Map<string, number>();
 
 function report_error(
-    msg,
+    msg: string,
     stack = "No stacktrace available",
-    {show_ui_msg = false, more_info} = {},
-) {
+    {show_ui_msg = false, more_info}: {show_ui_msg?: boolean; more_info?: unknown} = {},
+): void {
     if (page_params.development_environment) {
         // In development, we display blueslip errors in the web UI,
         // to make them hard to miss.
@@ -176,8 +175,8 @@ function report_error(
 
 class BlueslipError extends Error {
     name = "BlueslipError";
-
-    constructor(msg, more_info) {
+    more_info?: unknown;
+    constructor(msg: string, more_info: unknown) {
         super(msg);
         if (more_info !== undefined) {
             this.more_info = more_info;
@@ -185,7 +184,13 @@ class BlueslipError extends Error {
     }
 }
 
-export function exception_msg(ex) {
+export function exception_msg(
+    ex: Error & {
+        // Unsupported properties avaliable on some browsers
+        fileName?: string;
+        lineNumber?: number;
+    },
+): string {
     let message = ex.message;
     if (ex.fileName !== undefined) {
         message += " at " + ex.fileName;
@@ -197,38 +202,44 @@ export function exception_msg(ex) {
 }
 
 $(window).on("error", (event) => {
-    const ex = event.originalEvent.error;
+    const {originalEvent} = event;
+    if (!(originalEvent instanceof ErrorEvent)) {
+        return;
+    }
+
+    const ex = originalEvent.error;
     if (!ex || ex instanceof BlueslipError) {
         return;
     }
+
     const message = exception_msg(ex);
     report_error(message, ex.stack);
 });
 
-function build_arg_list(msg, more_info) {
-    const args = [msg];
+function build_arg_list(msg: string, more_info: unknown): [string, string?, unknown?] {
+    const args: [string, string?, unknown?] = [msg];
     if (more_info !== undefined) {
         args.push("\nAdditional information: ", more_info);
     }
     return args;
 }
 
-export function debug(msg, more_info) {
+export function debug(msg: string, more_info: unknown): void {
     const args = build_arg_list(msg, more_info);
     logger.debug(...args);
 }
 
-export function log(msg, more_info) {
+export function log(msg: string, more_info: unknown): void {
     const args = build_arg_list(msg, more_info);
     logger.log(...args);
 }
 
-export function info(msg, more_info) {
+export function info(msg: string, more_info: unknown): void {
     const args = build_arg_list(msg, more_info);
     logger.info(...args);
 }
 
-export function warn(msg, more_info) {
+export function warn(msg: string, more_info: unknown): void {
     const args = build_arg_list(msg, more_info);
     logger.warn(...args);
     if (page_params.development_environment) {
@@ -236,7 +247,7 @@ export function warn(msg, more_info) {
     }
 }
 
-export function error(msg, more_info, stack = new Error("dummy").stack) {
+export function error(msg: string, more_info: unknown, stack = new Error("dummy").stack): void {
     const args = build_arg_list(msg, more_info);
     logger.error(...args);
     report_error(msg, stack, {more_info});
@@ -251,7 +262,7 @@ export function error(msg, more_info, stack = new Error("dummy").stack) {
 
 export const timings = new Map();
 
-export function measure_time(label, f) {
+export function measure_time<T>(label: string, f: () => T): T {
     const t1 = performance.now();
     const ret = f();
     const t2 = performance.now();
@@ -264,8 +275,8 @@ export function measure_time(label, f) {
 // only used for including in error report emails; be sure to discuss
 // with other developers before using it in a user-facing context
 // because it is not XSS-safe.
-export function preview_node(node) {
-    if (node instanceof $) {
+export function preview_node(node: JQuery | HTMLElement): string {
+    if (!(node instanceof HTMLElement)) {
         node = node[0];
     }
 
diff --git a/static/js/global.d.ts b/static/js/global.d.ts
index 8e44d286fc..a4fefd55a9 100644
--- a/static/js/global.d.ts
+++ b/static/js/global.d.ts
@@ -10,5 +10,6 @@ interface JQuery {
 }
 
 interface Window {
+    last_stacktrace: string;
     page_params_parse_time: number;
 }
diff --git a/static/js/page_params.ts b/static/js/page_params.ts
index 11ef206fd8..6ebc9d41f2 100644
--- a/static/js/page_params.ts
+++ b/static/js/page_params.ts
@@ -8,7 +8,9 @@ export const page_params: {
         name: string;
         percent_translated: number | undefined;
     }[];
+    development_environment: boolean;
     request_language: string;
+    save_stacktraces: boolean;
     translation_data: Record<string, string>;
 } = $("#page-params").remove().data("params");
 const t2 = performance.now();
diff --git a/tools/linter_lib/custom_check.py b/tools/linter_lib/custom_check.py
index 779c7c79e0..7cde8e0e1f 100644
--- a/tools/linter_lib/custom_check.py
+++ b/tools/linter_lib/custom_check.py
@@ -190,7 +190,7 @@ js_rules = RuleList(
             "description": "Use channel module for AJAX calls",
             "exclude": {
                 # Internal modules can do direct network calls
-                "static/js/blueslip.js",
+                "static/js/blueslip.ts",
                 "static/js/channel.js",
                 # External modules that don't include channel.js
                 "static/js/stats/",
diff --git a/tools/test-js-with-node b/tools/test-js-with-node
index 1187d4fb0c..15aabe02c4 100755
--- a/tools/test-js-with-node
+++ b/tools/test-js-with-node
@@ -42,7 +42,7 @@ EXEMPT_FILES = {
     "static/js/attachments_ui.js",
     "static/js/avatar.js",
     "static/js/billing/helpers.js",
-    "static/js/blueslip.js",
+    "static/js/blueslip.ts",
     "static/js/blueslip_stacktrace.ts",
     "static/js/click_handlers.js",
     "static/js/compose_actions.js",