diff --git a/ts/html-filter/styling.ts b/ts/html-filter/styling.ts
index 6896268a5..bd3cea666 100644
--- a/ts/html-filter/styling.ts
+++ b/ts/html-filter/styling.ts
@@ -41,7 +41,7 @@ const filterStyling = (predicate: (property: string, value: string) => boolean)
     element: HTMLElement
 ): void => {
     for (const property of [...element.style]) {
-        const value = element.style.getPropertyValue(name);
+        const value = element.style.getPropertyValue(property);
 
         if (!predicate(property, value)) {
             element.style.removeProperty(property);
diff --git a/ts/package.json b/ts/package.json
index 303e38fb4..8586772fa 100644
--- a/ts/package.json
+++ b/ts/package.json
@@ -46,7 +46,7 @@
         "svelte2tsx": "^0.1.133",
         "tmp": "^0.2.1",
         "tslib": "^2.0.3",
-        "typescript": "^3.9.7",
+        "typescript": "^4.2.4",
         "uglify-js": "^3.13.1"
     },
     "scripts": {
diff --git a/ts/svelte/svelte.ts b/ts/svelte/svelte.ts
index 1a59ecb5e..41431aa46 100644
--- a/ts/svelte/svelte.ts
+++ b/ts/svelte/svelte.ts
@@ -100,7 +100,7 @@ function compile(tsPath: string, tsLibs: string[]) {
     return createdFiles[parsedCommandLine.fileNames[0].replace(".ts", ".d.ts")];
 }
 
-function writeFile(file, data) {
+function writeFile(file, data): Promise<void> {
     return new Promise((resolve, reject) => {
         fs.writeFile(file, data, (err) => {
             if (err) {
@@ -129,7 +129,7 @@ async function writeDts(tsPath, dtsPath, tsLibs) {
     await writeFile(dtsPath, dtsSource);
 }
 
-function writeTs(svelteSource, sveltePath, tsPath) {
+function writeTs(svelteSource, sveltePath, tsPath): void {
     let tsSource = svelte2tsx(svelteSource, {
         filename: sveltePath,
         strictMode: true,
@@ -187,7 +187,7 @@ async function compileSvelte(args) {
     const svelteSource = (await readFile(sveltePath)) as string;
 
     const mockTsPath = sveltePath + ".ts";
-    await writeTs(svelteSource, sveltePath, mockTsPath);
+    writeTs(svelteSource, sveltePath, mockTsPath);
     await writeDts(mockTsPath, dtsPath, tsLibs);
     await writeJs(svelteSource, sveltePath, mjsPath, cssPath, binDir, genDir);
 
diff --git a/ts/yarn.lock b/ts/yarn.lock
index 0f0b3569e..e1b574f9b 100644
--- a/ts/yarn.lock
+++ b/ts/yarn.lock
@@ -4348,16 +4348,11 @@ typedarray-to-buffer@^3.1.5:
   dependencies:
     is-typedarray "^1.0.0"
 
-typescript@*:
+typescript@*, typescript@^4.2.4:
   version "4.2.4"
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.2.4.tgz#8610b59747de028fda898a8aef0e103f156d0961"
   integrity sha512-V+evlYHZnQkaz8TRBuxTA92yZBPotr5H+WhQ7bD3hZUndx5tGOa1fuCgeSjxAzM1RiN5IzvadIXTVefuuwZCRg==
 
-typescript@^3.9.7:
-  version "3.9.9"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.9.9.tgz#e69905c54bc0681d0518bd4d587cc6f2d0b1a674"
-  integrity sha512-kdMjTiekY+z/ubJCATUPlRDl39vXYiMV9iyeMuEuXZh2we6zz80uovNN2WlAxmmdE/Z/YQe+EbOEXB5RHEED3w==
-
 uc.micro@^1.0.1, uc.micro@^1.0.5:
   version "1.0.6"
   resolved "https://registry.yarnpkg.com/uc.micro/-/uc.micro-1.0.6.tgz#9c411a802a409a91fc6cf74081baba34b24499ac"