diff --git a/package.json b/package.json
index 40064eb..fb8a15e 100644
--- a/package.json
+++ b/package.json
@@ -47,19 +47,19 @@
   },
   "homepage": "https://github.com/mljs/conrec#readme",
   "devDependencies": {
-    "@babel/plugin-transform-modules-commonjs": "^7.21.2",
-    "@babel/preset-typescript": "^7.21.4",
-    "@types/jest": "^29.5.1",
-    "eslint": "^8.38.0",
-    "eslint-config-cheminfo-typescript": "^11.3.1",
+    "@babel/plugin-transform-modules-commonjs": "^7.24.1",
+    "@babel/preset-typescript": "^7.24.1",
+    "@types/jest": "^29.5.12",
+    "eslint": "^8.57.0",
+    "eslint-config-cheminfo-typescript": "^12.4.0",
     "esm": "^3.2.25",
-    "jcampconverter": "^9.1.1",
-    "jest": "^29.5.0",
-    "prettier": "^2.8.7",
-    "rimraf": "^5.0.0",
-    "typescript": "^5.0.4"
+    "jcampconverter": "^9.6.4",
+    "jest": "^29.7.0",
+    "prettier": "^3.2.5",
+    "rimraf": "^5.0.5",
+    "typescript": "^5.4.5"
   },
   "dependencies": {
-    "cheminfo-types": "^1.7.1"
+    "cheminfo-types": "^1.7.3"
   }
 }
diff --git a/src/ContourBuilder.ts b/src/ContourBuilder.ts
index 9e68cab..f02c0ae 100644
--- a/src/ContourBuilder.ts
+++ b/src/ContourBuilder.ts
@@ -186,8 +186,8 @@ export class ContourBuilder {
     }
     if (ma === null && mb === null) {
       // both unmatched, add as new sequence
-      let aa: SequenceNode = { p: a, prev: null, next: null };
-      let bb: SequenceNode = { p: b, prev: null, next: null };
+      const aa: SequenceNode = { p: a, prev: null, next: null };
+      const bb: SequenceNode = { p: b, prev: null, next: null };
       aa.next = bb;
       bb.prev = aa;
       // create sequence element and push onto head of main list. The order
@@ -275,8 +275,8 @@ export class ContourBuilder {
 }
 
 function pointsEqual(a: Point, b: Point) {
-  let x = a.x - b.x;
-  let y = a.y - b.y;
+  const x = a.x - b.x;
+  const y = a.y - b.y;
   return x * x + y * y < Number.EPSILON;
 }
 
@@ -302,16 +302,16 @@ export interface Point {
   x: number;
   y: number;
 }
-export type SequenceNode = {
+export interface SequenceNode {
   p: Point;
   next: SequenceNode | null;
   prev: SequenceNode | null;
-};
+}
 
-type Sequence = {
+interface Sequence {
   head: SequenceNode;
   tail: SequenceNode;
   next: Sequence | null;
   prev: Sequence | null;
   closed: boolean;
-};
+}
diff --git a/src/ShapeContourDrawer.ts b/src/ShapeContourDrawer.ts
index bc25c24..85a5a12 100644
--- a/src/ShapeContourDrawer.ts
+++ b/src/ShapeContourDrawer.ts
@@ -102,11 +102,11 @@ export class ShapeContourDrawer {
   }
 
   getContour() {
-    let l: ShapeContour[] = [];
-    let a = this.contours;
+    const l: ShapeContour[] = [];
+    const a = this.contours;
     for (let k = 0; k < a.length; k++) {
       let s = a[k].s;
-      let level = a[k].level;
+      const level = a[k].level;
       while (s) {
         let h: SequenceNode | null = s.head;
         const l2: ShapeContour = { lines: [], level, k };
diff --git a/src/__tests__/shape.test.ts b/src/__tests__/shape.test.ts
index 82ab41b..2c44eb6 100644
--- a/src/__tests__/shape.test.ts
+++ b/src/__tests__/shape.test.ts
@@ -84,7 +84,7 @@ function parse(string: string) {
     .filter((line) => line);
 
   const matrix: number[][] = [];
-  for (let line of lines) {
+  for (const line of lines) {
     matrix.push(line.split('').map((value: string) => parseInt(value, 10)));
   }
   return matrix;
diff --git a/src/calculateContour.ts b/src/calculateContour.ts
index a95060b..3f4d724 100644
--- a/src/calculateContour.ts
+++ b/src/calculateContour.ts
@@ -185,10 +185,10 @@ export function calculateContour(
       return true;
     }
     for (let i = ilb; i < iub; i++) {
-      let dij = matrix[i][j];
-      let dij1 = matrix[i][j + 1];
-      let di1j = matrix[i + 1][j];
-      let di1j1 = matrix[i + 1][j + 1];
+      const dij = matrix[i][j];
+      const dij1 = matrix[i][j + 1];
+      const di1j = matrix[i + 1][j];
+      const di1j1 = matrix[i + 1][j + 1];
       let min1, min2, max1, max2;
       if (dij > dij1) {
         min1 = dij1;
@@ -204,8 +204,8 @@ export function calculateContour(
         min2 = di1j;
         max2 = di1j1;
       }
-      let dmin = Math.min(min1, min2);
-      let dmax = Math.max(max1, max2);
+      const dmin = Math.min(min1, min2);
+      const dmax = Math.max(max1, max2);
       // Ternary operator is now much slower: https://jsbench.me/d5l0dh502g
       //let dmin = min1 > min2 ? min2 : min1;
       //let dmax = max1 > max2 ? max1 : max2;
@@ -270,7 +270,7 @@ export function calculateContour(
               } else {
                 m3 = 1;
               }
-              let caseValue = castab[sh[m1] + 1][sh[m2] + 1][sh[m3] + 1];
+              const caseValue = castab[sh[m1] + 1][sh[m2] + 1][sh[m3] + 1];
               if (caseValue !== 0) {
                 switch (caseValue) {
                   case 1: // Line between vertices 1 and 2
diff --git a/src/index.ts b/src/index.ts
index 7cce9c7..9fc3a25 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -17,10 +17,10 @@ export type ContourDrawerName = 'basic' | 'shape';
 type ContourDrawerByName<DrawerName extends ContourDrawerName> =
   DrawerName extends 'basic' ? BasicContourDrawer : ShapeContourDrawer;
 
-export type DrawContourResult<DrawerName extends ContourDrawerName> = {
+export interface DrawContourResult<DrawerName extends ContourDrawerName> {
   contours: ReturnType<ContourDrawerByName<DrawerName>['getContour']>;
   timeout: boolean;
-};
+}
 
 export class Conrec {
   matrix: Readonly<NumberMatrix>;