diff --git a/addons/xterm-addon-webgl/src/atlas/WebglCharAtlas.ts b/addons/xterm-addon-webgl/src/atlas/WebglCharAtlas.ts
index dd95f17741..e409f51e60 100644
--- a/addons/xterm-addon-webgl/src/atlas/WebglCharAtlas.ts
+++ b/addons/xterm-addon-webgl/src/atlas/WebglCharAtlas.ts
@@ -238,7 +238,7 @@ export class WebglCharAtlas implements IDisposable {
           const bg = this._config.colors.background.css;
           if (bg.length === 9) {
             // Remove bg alpha channel if present
-            return bg.substr(0, 7);
+            return bg.slice(0, 7);
           }
           return bg;
         }
diff --git a/addons/xterm-addon-webgl/test/WebglRenderer.api.ts b/addons/xterm-addon-webgl/test/WebglRenderer.api.ts
index e6942d1cb8..7c6755da0d 100644
--- a/addons/xterm-addon-webgl/test/WebglRenderer.api.ts
+++ b/addons/xterm-addon-webgl/test/WebglRenderer.api.ts
@@ -260,9 +260,9 @@ describe('WebGL Renderer Integration Tests', async () => {
       for (let y = 0; y < 240 / 16; y++) {
         for (let x = 0; x < 16; x++) {
           const cssColor = COLORS_16_TO_255[y * 16 + x];
-          const r = parseInt(cssColor.substr(1, 2), 16);
-          const g = parseInt(cssColor.substr(3, 2), 16);
-          const b = parseInt(cssColor.substr(5, 2), 16);
+          const r = parseInt(cssColor.slice(1, 3), 16);
+          const g = parseInt(cssColor.slice(3, 5), 16);
+          const b = parseInt(cssColor.slice(5, 7), 16);
           await pollFor(page, () => getCellColor(x + 1, y + 1), [r, g, b, 255]);
         }
       }
@@ -280,9 +280,9 @@ describe('WebGL Renderer Integration Tests', async () => {
       for (let y = 0; y < 240 / 16; y++) {
         for (let x = 0; x < 16; x++) {
           const cssColor = COLORS_16_TO_255[y * 16 + x];
-          const r = parseInt(cssColor.substr(1, 2), 16);
-          const g = parseInt(cssColor.substr(3, 2), 16);
-          const b = parseInt(cssColor.substr(5, 2), 16);
+          const r = parseInt(cssColor.slice(1, 3), 16);
+          const g = parseInt(cssColor.slice(3, 5), 16);
+          const b = parseInt(cssColor.slice(5, 7), 16);
           await pollFor(page, () => getCellColor(x + 1, y + 1), [r, g, b, 255]);
         }
       }
@@ -300,9 +300,9 @@ describe('WebGL Renderer Integration Tests', async () => {
       for (let y = 0; y < 240 / 16; y++) {
         for (let x = 0; x < 16; x++) {
           const cssColor = COLORS_16_TO_255[y * 16 + x];
-          const r = parseInt(cssColor.substr(1, 2), 16);
-          const g = parseInt(cssColor.substr(3, 2), 16);
-          const b = parseInt(cssColor.substr(5, 2), 16);
+          const r = parseInt(cssColor.slice(1, 3), 16);
+          const g = parseInt(cssColor.slice(3, 5), 16);
+          const b = parseInt(cssColor.slice(5, 7), 16);
           await pollFor(page, () => getCellColor(x + 1, y + 1), [r, g, b, 255]);
         }
       }
@@ -320,9 +320,9 @@ describe('WebGL Renderer Integration Tests', async () => {
       for (let y = 0; y < 240 / 16; y++) {
         for (let x = 0; x < 16; x++) {
           const cssColor = COLORS_16_TO_255[y * 16 + x];
-          const r = parseInt(cssColor.substr(1, 2), 16);
-          const g = parseInt(cssColor.substr(3, 2), 16);
-          const b = parseInt(cssColor.substr(5, 2), 16);
+          const r = parseInt(cssColor.slice(1, 3), 16);
+          const g = parseInt(cssColor.slice(3, 5), 16);
+          const b = parseInt(cssColor.slice(5, 7), 16);
           await pollFor(page, () => getCellColor(x + 1, y + 1), [r, g, b, 255]);
         }
       }
@@ -356,9 +356,9 @@ describe('WebGL Renderer Integration Tests', async () => {
       for (let y = 0; y < 240 / 16; y++) {
         for (let x = 0; x < 16; x++) {
           const cssColor = COLORS_16_TO_255[y * 16 + x];
-          const r = parseInt(cssColor.substr(1, 2), 16);
-          const g = parseInt(cssColor.substr(3, 2), 16);
-          const b = parseInt(cssColor.substr(5, 2), 16);
+          const r = parseInt(cssColor.slice(1, 3), 16);
+          const g = parseInt(cssColor.slice(3, 5), 16);
+          const b = parseInt(cssColor.slice(5, 7), 16);
           await pollFor(page, () => getCellColor(x + 1, y + 1), [r, g, b, 255]);
         }
       }
diff --git a/bin/publish.js b/bin/publish.js
index 75de4b6841..a43b8cd406 100644
--- a/bin/publish.js
+++ b/bin/publish.js
@@ -104,11 +104,11 @@ function getNextBetaVersion(packageJson) {
     return `${nextStableVersion}-${tag}.1`;
   }
   const latestPublishedVersion = publishedVersions.sort((a, b) => {
-    const aVersion = parseInt(a.substr(a.search(/\d+$/)));
-    const bVersion = parseInt(b.substr(b.search(/\d+$/)));
+    const aVersion = parseInt(a.slice(a.search(/\d+$/)));
+    const bVersion = parseInt(b.slice(b.search(/\d+$/)));
     return aVersion > bVersion ? -1 : 1;
   })[0];
-  const latestTagVersion = parseInt(latestPublishedVersion.substr(latestPublishedVersion.search(/\d+$/)), 10);
+  const latestTagVersion = parseInt(latestPublishedVersion.slice(latestPublishedVersion.search(/\d+$/)), 10);
   return `${nextStableVersion}-${tag}.${latestTagVersion + 1}`;
 }
 
diff --git a/src/browser/Terminal.test.ts b/src/browser/Terminal.test.ts
index 872bfdc70b..d039b17b88 100644
--- a/src/browser/Terminal.test.ts
+++ b/src/browser/Terminal.test.ts
@@ -1332,8 +1332,8 @@ describe('Terminal', () => {
           (!(i % 3))
             ? input[i]
             : (i % 3 === 1)
-              ? input.substr(i, 2)
-              : input.substr(i - 1, 2),
+              ? input.slice(i, i + 2)
+              : input.slice(i - 1, i + 1),
           terminal.buffer.lines.get(bufferIndex[0])!.loadCell(bufferIndex[1], new CellData()).getChars());
       }
     });
diff --git a/src/browser/renderer/CustomGlyphs.ts b/src/browser/renderer/CustomGlyphs.ts
index 7756279003..c2bfc21089 100644
--- a/src/browser/renderer/CustomGlyphs.ts
+++ b/src/browser/renderer/CustomGlyphs.ts
@@ -414,10 +414,10 @@ function drawPatternChar(
     let b: number;
     let a: number;
     if (fillStyle.startsWith('#')) {
-      r = parseInt(fillStyle.substr(1, 2), 16);
-      g = parseInt(fillStyle.substr(3, 2), 16);
-      b = parseInt(fillStyle.substr(5, 2), 16);
-      a = fillStyle.length > 7 && parseInt(fillStyle.substr(7, 2), 16) || 1;
+      r = parseInt(fillStyle.slice(1, 3), 16);
+      g = parseInt(fillStyle.slice(3, 5), 16);
+      b = parseInt(fillStyle.slice(5, 7), 16);
+      a = fillStyle.length > 7 && parseInt(fillStyle.slice(7, 9), 16) || 1;
     } else if (fillStyle.startsWith('rgba')) {
       ([r, g, b, a] = fillStyle.substring(5, fillStyle.length - 1).split(',').map(e => parseFloat(e)));
     } else {