Using PHP is_callable() to Check Callable Functions and Methods

In PHP, you can verify whether a function or method can be invoked by using the is_callable() function.

The is_callable() function takes a single argument—the variable to check—and returns true if the variable is callable, otherwise false.

Below is a simple example that defines a function testFunction(), assigns its name and a non‑existent method name to variables, and uses is_callable() to test each:

<?php

function testFunction() {
  echo "Hello, world!";
}

$functionName = 'testFunction';
$methodName   = 'nonExistent';

echo "functionName is callable? ";
if (is_callable($functionName)) {
  echo "Yes";
} else {
  echo "No";
}

echo "<br>";

echo "methodName is callable? ";
if (is_callable($methodName)) {
  echo "Yes";
} else {
  echo "No";
}
?>

The script outputs:

functionName is callable? Yes
methodName is callable? No

Since testFunction() exists, $functionName is callable and is_callable($functionName) returns true. The variable $methodName refers to a non‑existent method, so is_callable($methodName) returns false.

Beyond functions and methods, is_callable() can also check class constructors and static methods, making it useful for writing more robust code by verifying callability before invocation.

Overall, is_callable() is a valuable PHP function that helps developers determine whether a variable can be called, allowing them to handle potential errors gracefully.