Merge pull request #3890 from vitiral/ts-fixes

[typescript/en-us] add type to Point.dist and fix error

typescript.html.markdown

@@ -114,7 +114,7 @@ class Point {
   }
 
   // Functions
-  dist() { return Math.sqrt(this.x * this.x + this.y * this.y); }
+  dist(): number { return Math.sqrt(this.x * this.x + this.y * this.y); }
 
   // Static members
   static origin = new Point(0, 0);
@@ -137,7 +137,7 @@ class Point3D extends Point {
   }
 
   // Overwrite
-  dist() {
+  dist(): number {
     let d = super.dist();
     return Math.sqrt(d * d + this.z * this.z);
   }