If you’re into WordPress development, you can’t ignore hooks for long before you have to delve into them head on. Modifying WordPress core files is a big no-no, so whenever you want to change existing functionality or create new functionality, you will have to turn to hooks.
In this article, I would like to dispel some of the confusion around hooks, because not only are they the way to code in WordPress, but they also teach us a great design pattern for development in general. Explaining this in depth will take a bit of time, but bear with me: by the end, you’ll be able to jumble hooks around like a pro.
Why Hooks Exist
I think the most important step in grasping hooks is to understand the need for them. Let’s create a version of a WordPress function that already exists, and then evolve it a bit using the “hooks mindset.”
function get_excerpt($text, $length = 150) {
$excerpt = substr($text,$length)
return $excerpt;
}
This function takes two parameters: a string and the length at which we want to cut it. What happens if the user wants a 200-character excerpt instead of a 150-character one? They just modify the parameter when they use the function. No problem there.
If you use this function a lot, you will notice that the parameter for the text is usually the post’s content, and that you usually use 200 characters instead of the default 150. Wouldn’t it be nice if you could set up new defaults, so that you didn’t have to add the same parameters over and over again? Also, what happens if you want to add some more custom text to the end of the excerpt?
These are the kinds of problems that hooks solve. Let’s take a quick look at how.
function get_excerpt($text, $length = 150) {
$length = apply_filters("excerpt_length", $length);
$excerpt = substr($text,$length)
return $excerpt;
}
As you can see, the default excerpt length is still 150, but we’ve also applied some filters to it. A filter allows you to write a function that modifies the value of something — in this case, the excerpt’s length. The name (or tag) of this filter is excerpt_length, and if no functions are attached to it, then its value will remain 150. Let’s see how we can now use this to modify the default value.
function get_excerpt($text, $length = 150) {
$length = apply_filters("excerpt_length");
$excerpt = substr($text,$length)
return $excerpt;
}
function modify_excerpt_length() {
return 200;
}
add_filter("excerpt_length", "modify_excerpt_length");
First, we have defined a function that does nothing but return a number. At this point, nothing is using the function, so let’s tell WordPress that we want to hook this into theexcerpt_length filter.
We’ve successfully changed the default excerpt length in WordPress, without touching the original function and without even having to write a custom excerpt function. This will be extremely useful, because if you always want excerpts that are 200 characters long, just add this as a filter and then you won’t have to specify it every time.
Suppose you want to tack on some more text, like “Read on,” to the end of the excerpt. We could modify our original function to work with a hook and then tie a function to that hook, like so:
function get_excerpt($text, $length = 150) {
$length = apply_filters("excerpt_length");
$excerpt = substr($text,$length)
return apply_filters("excerpt_content", $excerpt);
}
function modify_excerpt_content($excerpt
