Why Arrays Behave Differently in PHP, Python, and JavaScript

PHP, Python, and JavaScript handle arrays in fundamentally different ways that can cause hard-to-trace bugs, especially for developers working across all three languages. PHP copies arrays by default using copy-on-write semantics, meaning a function receives an independent copy unless a reference is explicitly requested with the ampersand operator. Python lists are reference types, so assigning a list to a new variable or passing it to a function points both names at the same object, and any mutation affects the original. JavaScript arrays behave similarly to Python in that they are passed by reference, but the const keyword misleads many developers — it prevents reassignment of the variable, not mutation of the array's contents. Awareness of these distinctions, and using explicit copying mechanisms like Python's deepcopy or JavaScript's spread operator, is essential to avoid subtle data corruption bugs in multi-language codebases.