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Javascript – Can somebody please explain this react code to me? I can't seem to wrap my head around it

function handleChecking(index) {
    const updatedTasks = tasks.map((task, i) =>
      i === index ? { ...task, checked: !task.checked } : task
    );

    updatedTasks.push(updatedTasks.splice(index, 1)[0]);

    
> if (!updatedTasks[updatedTasks.length - 1].checked) {
> updatedTasks.unshift(updatedTasks.pop());
>     }

    setTasks(updatedTasks);
  }

I need thorough explanation of the quoted code because I don’t get it. The code was provided by ChatGpt and my todo-app works as I expected but I don’t know why. Every task has a checkbox next to it and when I check that checkbox it moves to the end of an table of tasks(end of an array). That part I understand. Let’s say I have 4 unchecked tasks at the beggining and 3 checked tasks at the end. When I uncheck the second to last task it goes to the top of the table(start of an array). From my understanding of the code it should not work like that. It should pop() only the last one since pop does that right? Anyways I tried asking chatGPT the same question and he than says I am correct and he refactors the code. And I am not gonna touch my code because it works as I expected. Please help because I want to know. I gotta know! I can’t go around saying I have a functional app without knowing how everything inside it works.

I hope I provided enough code. If not, please say what more should I add. But I think this should be understandable to experienced developers.

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3

Answers


  1. 0 
    function handleChecking(index) {
    // Toggle task state
    const updatedTasks = tasks.map((task, i) =>
        i === index ? { ...task, checked: !task.checked } : task
    );

    // Move toggled task to the end
    updatedTasks.push(updatedTasks.splice(index, 1)[0]);

    // If the moved task is unchecked, move it to the top
    if (!updatedTasks[updatedTasks.length - 1].checked) {
        updatedTasks.unshift(updatedTasks.pop());
    }

    // Update display
    setTasks(updatedTasks);
}

    This code focuses on the key steps:

    Toggle task state.
    Move the toggled task to the end.
    If the moved task is unchecked, move it to the top.
    Update the display with the new task arrangement.

    Overall, this function handles toggling the checked state of tasks and ensures consistent ordering of unchecked tasks at the beginning of the array.

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  2. 0

    Here’s how I, a human, would implement that function. It’s less computation and easier to understand (in my opinion beep boop):

    function handleChecking(index) {
    const target = tasks[index];
    target.checked = !target.checked;
    const first = !target.checked;

    const updatedTasks = [];
    if (first)
      updatedTasks.push(target);

    for (let i = 0; i < tasks.length; ++i)
      if (i !== index)
        updatedTasks.push(tasks[i]);

    if (!first)
      updatedTasks.push(target);

    setTasks(updatedTasks);
}

    Only one loop, only one new array created, no new objects created, no splicing, no unshifting, also clearer. In my opinion.

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  3. 0 
        function handleChecking(index) {
      //A checking task handler
        const updatedTasks = tasks.map((task, i) =>
        //checks for index which matches 'index' parmateter
          i === index ? { ...task, checked: !task.checked } : task
          //if it finds the exactly the option that user checked then returns the current task edited {...task, checked:!task.checked} means it returns the task with all its properties and edit the checked to false of the current state that means if the current option is checked then it unselect that and if it is not then selects that. If the current index doesn't match the 'index' parameter then returns task meaning current option unedited.
        );
    
        updatedTasks.push(updatedTasks.splice(index, 1)[0]);
        //It pushes the checked task to the last of the list. First splice() method deletes the element by taking index of the item and number of elements to delete as parameter. Here index means the current option's index and 1 means only one element needs to be deleted from 'index' serial. splice() returns an array containing the deleted element. Here it returns the array of only one element which is the current option. To get the element [0] used to define the first element of the returned array. push() pushes the element to the last of the list.
    
        
    > if (!updatedTasks[updatedTasks.length - 1].checked) {
    ///checks if the last task is checked or not if not then pushes that to the beginning of the tasks using unshift() and removing it from the last using pop(). pop() returns the element that was removed and unshift() takes the element as parameter which is to be added at the beginning.
    > updatedTasks.unshift(updatedTasks.pop());
    >     }
   
        setTasks(updatedTasks);
        //This is most important mentioned in your code updating the task. using useState updates the state for tasks this one of the coolest feature from ReactJS. I'm enclosing proper links that is helpful for you. here
      }

    Some useful links:

    1. pop()

    2.push()

    3.splice()

    1. unshift()

    2. useState() hook

    Hope you find it helpful.

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