Unable to mutate Javascript Array inside a promise

Question

I am facing a strange problem in my javascript code, I have function that returns a promise that contains all the tasks. Each task has a property project and this property contains an integer. Now, I want to fetch project by calling another function that also returns a promise so that I can convert the project property to a Project object. But when I try to that I get this error

Unhandled Promise Rejection: TypeError: Attempted to assign to readonly property.

Here is my code


const allByProject = async (project: Project) : Promise<Task[]> => {
    const  allTasks = await TaskStore.allByProject(project);
    allTasks.forEach(async (task: Task, i) => {
        // In this case tasks return contains a project id instead of the project object
        let projecId: any = task.project;
        const project = await ProjectService.getById(projecId);
        allTasks[i].project = project;  // THIS GENERATES the ERROR.
    });
    console.log('All tasks: ', allTasks);
    return allTasks;
}

There is an error in the promise function that needs to handle. Try to add `.catch` to handle errors — Mohamed EL-Gendy, Jul 20 '22 at 02:24
Apparently, `allTasks[i].project` is a readonly property. :) As we have no idea what `TaskStore.allByProject` does, it is impossible to say how to resolve this, except "don't assign values to readonly properties". — Amadan, Jul 20 '22 at 02:26
Then what's the alternative here, do you have any suggestion? — Aftab Naveed, Jul 20 '22 at 02:33
@Yimin I tried that but I think it still needs wait for this to be resolved `await ProjectService.getById(projecId);` — Aftab Naveed, Jul 20 '22 at 02:59
Yeah, wait for that, and then do allTasks[i] = {...allTasks[i], project: project} — Yimin, Jul 20 '22 at 03:03
The suggested question does not modify a global array inside a promise, how is that question related? — Aftab Naveed, Jul 20 '22 at 03:18

Unable to mutate Javascript Array inside a promise

0 Answers0