typescript: omit example

typescript/typing/omit.ts

@@ -0,0 +1,59 @@
+// This example will show how you can create a new type by modifying an existing type and omitting certain keys.
+// This is useful for when you have similar interfaces apart from a single key
+
+/**
+ * Generic range type
+ */
+interface range {
+  start: number;
+  end: number;
+}
+
+/**
+ * Your original interface, with all properties
+ */
+interface Test {
+  a: range;
+  b: number;
+  c: boolean;
+}
+
+/**
+ * The new interface, it extends the old interface (Test) but Omits (ignores) 1 property ("a")
+ * Then we add 2 new properties.
+ * Final structure is similar to:
+ *
+ * {
+ *   b: number;
+ *   c: boolean;
+ *   start: number;
+ *   end: number;
+ * }
+ */
+interface MyTest extends Omit<Test, "a"> {
+  start: number;
+  end: number;
+}
+
+/**
+ * Instance of our first interface
+ */
+const data: Test = {
+  a: { start: 0, end: 5 },
+  b: 5,
+  c: true,
+};
+
+/**
+ * Instance of our modified interface
+ */
+const data2: MyTest = {
+  // properties from original interface
+  // a: "test", // this is invalid, type doesn't contain a...
+  b: data.b,
+  c: data.c,
+
+  // properties we added to myTest
+  start: data.a.start,
+  end: data.a.end,
+};