Fundamentals / Functions
Functions
Reusable blocks of behavior — declared, expressed, or arrow-shaped.
A function packages a block of code under a name so it can run whenever it's called, with different inputs each time. Function declarations are hoisted (usable before their line); function expressions and arrow functions are not. Parameters can have defaults, and `...rest` gathers any extra arguments into an array.
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Why?
Default parameters only kick in when an argument is undefined or omitted entirely — passing null still overrides the default.