javascript - Update single value in item array | react redux

Question

I have a todo list and want to set the state of that item in the array to "complete" if the user clicks on "complete".

Here is my action:

export function completeTodo(id) {
    return {
        type: "COMPLETE_TASK",
        completed: true,
        id
    }
}

Here is my reducer:

case "COMPLETE_TASK": {
             return {...state,
                todos: [{
                    completed: action.completed
                }]
             }
        }

The problem I'm having is the new state does no longer have the text associated of that todo item on the selected item and the ID is no longer there. Is this because I am overwriting the state and ignoring the previous properties? My object item onload looks like this:

Objecttodos: Array[1]
    0: Object
        completed: false
        id: 0
        text: "Initial todo"
    __proto__: Object
    length: 1
    __proto__: Array[0]
    __proto__: Object

As you can see, all I want to do is set the completed value to true.

Answer 1

You need to transform your todos array to have the appropriate item updated. Array.map is the simplest way to do this:

case "COMPLETE_TASK":
    return {
        ...state,
        todos: state.todos.map(todo => todo.id === action.id ?
            // transform the one with a matching id
            { ...todo, completed: action.completed } : 
            // otherwise return original todo
            todo
        ) 
    };

There are libraries to help you with this kind of deep state update. You can find a list of such libraries here: https://github.com/markerikson/redux-ecosystem-links/blob/master/immutable-data.md#immutable-update-utilities

Personally, I use ImmutableJS (https://facebook.github.io/immutable-js/) which solves the issue with its updateIn and setIn methods (which are more efficient than normal objects and arrays for large objects with lots of keys and for arrays, but slower for small ones).