How can we ensure that an object only contains properties defined in its interface when passing it through angular.toJson?

Ensuring Object Compliance with Interface: Removing Extraneous Properties

TypeScript interfaces define contract specifications for classes or objects. However, during implementation, additional properties may be added beyond those defined by the interface, leading to inconsistencies. Addressing this issue becomes crucial, especially when passing reduced objects through angular.toJson for RESTful communication.

Consider an interface MyInterface with a single property test:

<code class="typescript">interface MyInterface {
  test: string;
}</code>

And its implementation with an additional property newTest:

<code class="typescript">class MyTest implements MyInterface {
  test: string;
  newTest: string;
}</code>

Question:

How can we ensure that the reduced object, when assigned from an object like MyTest, only contains the properties declared in MyInterface, excluding newTest?

Answer:

Unfortunately, it's not feasible to directly strip extraneous properties from an object at runtime based solely on an interface definition. Interfaces in TypeScript serve as a design-time construct, and their properties aren't readily available at execution.

One potential solution suggested is to define the "interface" as a class, thereby providing a runtime implementation. This allows us to leverage Lodash to select only the desired properties from the input object:

<code class="typescript">class MyInterface {
  test: string = undefined;
}</code>

<code class="typescript">import _ from 'lodash';

const before = { test: "hello", newTest: "world"};
let reduced = new MyInterface();
_.assign(reduced , _.pick(before, _.keys(reduced)));
console.log('reduced', reduced)//contains only 'test' property</code>

By employing this method, we can effectively extract the specified properties, creating an object that adheres to the interface contract and is ready for serialization via angular.toJson.

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