encode/decode base64 with JS

Encoding to base64 is done with the btoa command

btoa("This is a test.")
> "VGhpcyBpcyBhIHRlc3Qu"

To decode a base64 encoded string, use the atob command

atob("VGhpcyBpcyBhIHRlc3Qu")
> "This is a test."

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Spread Operator for Objects

Using the spread operator during an Object declaration will assign the properties of the referenced Object to the new Object.

How to combine two sorted arrays into one? We can do this easily with the spread operator.

Use flatMap() creates a new array with sub-array elements flattened by specified depth.