Utility types let you create types based on other types. Have a look at the official TypeScript page for example about utility types.

Omit property from type

Omit allows you to create a new type based on an existing type, but specify properties of the existing type that you want to have omitted in the new type (don’t mix that up with Exclude):

Omit<{ a: string, b:string }, 'a' > === { b: string }

Omit is the opposite of Pick.

Pick<{ a: string, b:string }, 'a' > === { a: string } 

Exclude is different from Omit, because it takes a union type and removes a constituent of that union.

Exclude<string | number, string > === number

Partial<T>

setTextLayerProps is a function that takes props and sets them on an object. Using Partial<T> (which is a build-in TypeScript feature) we can specify that only props of a specific type are allowed to be passed in as props. In the following example we only allow props from TextLayer.

function setTextLayerProps(project: Project, id: string, props: Partial<TextLayer>) {
  const layer = project.layers.find(l => l.id === id);

  if(layer) {
    Object.entries(props).forEach(([k, v]) => {
      (layer as any)[k] = v;
    });
  }
}

const project: Project = {
  layers: [imageLayer, textLayer],
  size: projectSize
};

setTextLayerProps(project, "10", {
  text: "hello",
  shouldNotWork: true // Good: TypeScript complains, that shouldNotWork is not part of the props of TextLayer
});

We can improve this example and make it more variable: We want to allow props depending on the generic type: If we define TextLayer, then only allow props from TextLayer, if we define ImageLayer, then only allow props from ImageLayer:

function setLayerProps<T extends TextLayer | ImageLayer>(project: Project, id: string, props: Partial<T>) {
  const layer = project.layers.find(l => l.id === id);

  if(layer) {
    Object.entries(props).forEach(([k, v]) => {
      (layer as any)[k] = v;
    });
  }
}

const project: Project = {
  layers: [imageLayer, textLayer],
  size: projectSize
};

setLayerProps<TextLayer>(project, "10", {
  text: "hello" // Good: only TextLayer props are allowed
});

setLayerProps<ImageLayer>(project, "20", {
  src: "some image source" // Good: only ImageLayer props are allowed
});

setLayerProps<ImageLayer>(project, "30", {
  src: "some image source",
  shouldNotWork: true  // Good, compiler complains
});