How do you copy by value a composite data type?

There are 3 ways to copy by value for composite data types.
Using the spread (…) operator
Using the Object.assign() method
Using the JSON.stringify() and JSON.parse() methods

1. Using Spread
Spread operator allows an iterable to expand in places where 0+ arguments are expected.
It is mostly used in the variable array where there is more than 1 values are expected.
It allows us the privilege to obtain a list of parameters from an array.Using spread will
clone your object. Note this will be a shallow copy.
For example :
var a = [1,2,4];
var c = […a];

console.log(c); // [1,2,4]

Even if you change the value,
c[2] = 5
console.log(a,c);//[1,2,4] [1,2,5];

because value is passed and not the reference of the variable

2. Using Object.assign()
The Object.assign() method copies all enumerable own properties from one or more source
objects to a target object. It returns the target object. Note this will be a shallow copy.

For example:
var a = [1,2,3]
var b = Object.assign([],a)
console.log(a,b) // [1,2,3] [1,2,3]

3. Using JSON.parse() and JSON.stringify()
The JSON object, available in all modern browsers, has two useful methods to deal with
JSON-formatted content: parse and stringify. JSON.parse() takes a JSON string and transforms
it into a JavaScript object. JSON.stringify() takes a JavaScript object and transforms it into
a JSON string.Using JSON.parse() and JSON.stringify() for copy performs deep copy .

For example:
var a = [1,2,3]
var b= JSON.parse(JSON.stringify(a));

console.log(a,b);//[1,2,3] [1,2,3]