The Differences in Truthiness and Falsiness in JavaScript vs PHP

Conditional statements are fundamental to any programming language. However, the way JavaScript and PHP handle "truthiness" and "falsiness"—determining whether a value is considered true or false in a conditional—differs significantly. This article explores these differences, focusing on empty arrays and objects, and their practical implications for web developers.

JavaScript's Truthiness and Falsiness

JavaScript's approach to truthiness is less intuitive than PHP's for many developers. It considers several values as "falsy":

const value1 = false;     // Boolean false
const value2 = 0;         // Number zero
const value3 = "";        // Empty string
const value4 = null;      // null
const value5 = undefined; // undefined
const value6 = NaN;       // Not a Number

This also applies to reactive references in frameworks like Vue.js:

const ref1 = ref(false);
const ref2 = ref(0);
const ref3 = ref("");
const ref4 = ref(null);
const ref5 = ref(undefined);
const ref6 = ref(NaN);

Surprisingly, empty arrays and objects are considered "truthy":

const value7 = [];        // Empty array
const value8 = {};        // Empty object
const value9 = "0";       // String "0"

The Memory Explanation

In JavaScript, empty arrays and objects are truthy because they represent valid memory references. Even though empty, they still occupy memory space.

// Arrays and Objects are memory references
const emptyArray = [];    // Valid memory reference
const emptyObject = {};   // Valid memory reference

Boolean([])  // true
Boolean({})  // true
Boolean(0)         // false
Boolean("")        // false
Boolean(null)      // false
Boolean(undefined) // false

This design choice stems from the fact that empty arrays and objects are still usable data structures. A reference, even to an empty container, differs from the absence of any value (null/undefined).

PHP's Approach

PHP adopts a more straightforward approach, treating empty data structures as "falsy." This is a key difference from JavaScript.

// Empty array is falsy
$emptyArray = [];
if (!$emptyArray) {
    echo "Empty array is false"; // This will print
}

// Empty object is also falsy
$emptyObject = new stdClass();
if (!$emptyObject) {
    echo "Empty object is false"; // This will print
}

Other falsy values in PHP include false, 0, 0.0, "", null, and empty arrays.

Explicit Empty Checks in JavaScript

To reliably check for empty arrays or objects in JavaScript, explicit checks are necessary:

//For an array
[].length === 0              // true

//For an object
Object.keys({}).length === 0 // true

For reactive references:

const arrayRef = ref([]);
const objectRef = ref({});

if (arrayRef.value.length === 0) {
    console.log('Array is empty');
}

if (Object.keys(objectRef.value).length === 0) {
    console.log('Object is empty');
}

Empty Checks in PHP

PHP's simpler approach makes conditional logic cleaner:

$emptyArray = [];
$emptyObject = new stdClass();

if (!$emptyArray) {
    echo "This will execute because empty arrays are falsy\n";
}

if (!$emptyObject) {
    echo "This will execute because empty objects are falsy\n";
}

PHP's empty() Function

PHP's empty() function provides a convenient way to check for emptiness, including undefined variables:

empty("");        // true
empty(0);        // true
empty([]);       // true
empty(new stdClass()); // true

empty() is a language construct, not a function, so it cannot be used as a callback. isset(), while useful for checking variable existence, can trigger warnings if used incorrectly with non-arrays.

Practical Implications

The contrasting approaches necessitate different coding styles. JavaScript demands explicit emptiness checks, potentially increasing code verbosity but improving clarity. PHP's approach offers concise code but may require extra checks for specific empty value types. Developers must be mindful of these differences when working with both languages, especially in cross-platform projects.

This understanding is crucial for developers bridging JavaScript and PHP, particularly those using frameworks like Laravel with React or Vue.js. Careful consideration of these nuances ensures reliable and predictable code behavior.

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