Leverage promises to alter reactive data, strategically placing them to minimize the frequency of triggers being activated

Initial Method

    const list = reactive([1, 2, 3, 4, 5]); 
    const clickHandler = () =>{
        list.push(...[11, 12, 13, 14, 15]);
        list.push(...[16, 17, 18, 19, 20]);
        Promise.resolve().then(() => {
            list.push(33)
        });
        
    };

Alternative Method

    const list = reactive([1, 2, 3, 4, 5]);
    const clickHandler = ()=>{
        Promise.resolve().then(() => {
            list.push(33)
        });
        list.push(...[11, 12, 13, 14, 15]);
        list.push(...[16, 17, 18, 19, 20]);
    };

The first approach results in two triggers of vue hooks onUpdated, while the second only triggers once. Can anyone explain why this difference occurs? Thank you.

Answer №1

Vue operates by updating data in a synchronous manner, collecting all changes to be processed in a microtask. If there is another microtask (such as Promise.resolve()) in your code, the order in which they are created can impact the sequence of events. In the first scenario, the vue-microtask is established before the Promise.resolve(), causing the Promise.resolve() to execute after the Vue update function, triggering another Vue update afterwards.

In the second scenario, the vue-microtask is set up after the Promise.resolve(), ensuring that the Promise has already been resolved by the time the vue-microtask runs. This allows any modifications to the list to be seamlessly integrated into the vue-microtask processing.

Answer №2

Vue's efficiency is due to its optimization mechanism that utilizes nextTick to batch updates.

In the initial method, multiple values are added to a reactive array, triggering the onUpdate hook once. Then, a separate cycle resolves the Promise, causing another trigger of onUpdate.

However, in the second method, the Promise resolves before any value additions to the array take place. This results in only one trigger of the onUpdate hook as Vue's reactivity detects and processes all operations within a single tick.

For more information: Learn why Vue updates only once when two close data mutations occur.

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