An action should modify the state. To do that, we will first create three helper functions. One to modify a part of an object, one to modify a part of an array, and one to easily create a new array.
We use the same update function as we did in
Chapter 3, Note-Taking App with a Server. We add this function to lib/model/utils.ts.
export function update<U extends V, V>(old: U, changes: V): U {
const result = Object.create(Object.getPrototypeOf(old));
for (const key of Object.keys(old)) {
result[key] = (<any> old)[key];
}
for (const key of Object.keys(changes)) {
result[key] = (<any> changes)[key];
}
return result;
}
We also create a function that changes the element at a certain index of an array. The other elements will remain at the same location. We will use this function to change the content of a field of the spreadsheet later on.
export function updateArray<U>(array:...