JavaScript: Pass by Reference or Value
Does JavaScript pass by references or pass by values?
JavaScript employs a hybrid approach, passing primitives by value and objects (including arrays) by "copy of a reference."
Understanding Value-Passing
Primitive data types (e.g., strings, numbers, booleans) are duplicated and passed as independent values. Changing the value of a passed primitive in a function does not affect the original variable.
Understanding Reference-Passing
Objects reference memory addresses, and when passed, they refer to the same object as the caller. Changes made to the object's contents in a function will be reflected in the original object. However, assigning a new reference (e.g., ref = {}) will only modify the local copy of the reference, not the original.
Example Usage
In the provided code snippet:
- shape function takes a config object, extracts properties, and returns a new object.
- rectangle function extends shape by introducing additional properties and returning a new object.
- Primitive property name (in myShape and myRec) remains unaffected in the functions, as it passes by value.
- Object property my (in myRec) represents a copied reference to the original object, allowing modification of its contents (e.g., my.l and my.w). Assigning a new reference would not affect the original object.
- The area() functions use the local references to my to calculate and access the updated object properties.
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