Value vs. Reference

Data is stored to variables in two manners, by value and by reference. In addition, variables are passed to functions by value or by reference.

Value:

• The data of a variable is copied to other variables, or passed in to functions
• Changing the data of copied variables does not change the data of the original variable
• strings, numbers, booleans, undefined, and null are examples that use this type of assignment

Reference:

• The variable points to a place in memory
• Copying variables copies the location in memory to the second variable
• Changing the data of one variable affects all variables that have the reference
• This applies to objects and arrays

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For more information on this topic, check out this blog post.