The sequence in which functions are executed when bound to an event in JavaScript

Question

The sequence in which functions are executed when bound to an event in JavaScript

Recently, I found myself diving into the world of JavaScript to uncover details about how functions bound to a page event are executed. Take, for instance, when using an EventListener.

Let's say you bind three functions - A(), B(), and C() - to the same event (like DOMContentLoaded). How does JavaScript decide the order in which these functions will run? Are they executed one by one based on the order of their addEventListener calls in the JS code? Or do they all run simultaneously?

Furthermore, is it possible to change this execution order? Can we make sure that a particular function, attached to a DOMContentLoaded event listener, runs before any other function tied to the same event?

javascript dom browser

Answer 1

Answer №1

Event handlers are always triggered in the order they were added.

Once added, you cannot add more handlers before them[*].

[*] unless you somehow manage to get a list of all the handlers and their EventListener objects, then use removeEventListener to remove them, add your own, and finally reinsert the original handlers. This is likely to be extremely difficult in practice.

Answer 2

Event handlers are always triggered in the order they were added.

Once added, you cannot add more handlers before them[*].

[*] unless you somehow manage to get a list of all the handlers and their EventListener objects, then use removeEventListener to remove them, add your own, and finally reinsert the original handlers. This is likely to be extremely difficult in practice.

Answer 3

Answer №2

const eventListeners = [];

// Execute listeners in any desired order

document.addEventListener("DOMContentLoaded", function(event) {
    for (let i = 0; i < eventListeners.length; i++) {
        eventListeners[i]();
    }
});

Answer 4

const eventListeners = [];

// Execute listeners in any desired order

document.addEventListener("DOMContentLoaded", function(event) {
    for (let i = 0; i < eventListeners.length; i++) {
        eventListeners[i]();
    }
});

The sequence in which functions are executed when bound to an event in JavaScript

Answer №1

Answer №2

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