What will happen if you use -1 action priority for the WordPress hook?

In WordPress, the action priority determines the order in which functions associated with a particular action hook are executed. The default priority is 10, and lower numbers correspond to earlier execution, while higher numbers correspond to later execution.

Suppose you set an action priority to -1 for a WordPress hook. In that case, the function associated with that hook will be executed very early, before functions with the default priority (10) or any higher priorities. Priorities can be negative, allowing for execution before even the earliest normal priority (0). This can be useful if you need your function to run before almost everything else.

Check out this example of how you could use a priority of -1:

add_action( 'init', 'your_custom_function', -1 );

function your_custom_function() {
    // Your code here
}

In this example, your_custom_function will run very early in the init hook, potentially before most other functions hooked to init.

Note: Please be cautious when using a very low priority (like -1) as it may cause your function to run before essential WordPress core functions or other plugin functions that are expected to run early. This could lead to unexpected behavior or conflicts. Always conduct thorough testing to ensure that your hook’s priority doesn’t introduce issues.