The Javascript Float64Array represents an array of 64-bit floating-point numbers in the platform byte order. By default, the contents of Float64Array are initialized with 0. 

The float64Array.from() method is used to create a new Float64Array from an array-like or iterable object. So when you want to convert an arrayLike or iterable object to Float64Array then you can use this function by passing the object as a parameter to this function along with the map function and value used for the map function if needed.

Syntax:  

Float64Array.from( source, mapFn, thisArg )

Parameters: This method accepts three parameters as mentioned above and described below:  

• source: This parameter holds an array-like or iterable object which is used to convert into a Float64Array object.
• mapFn: This parameter is optional and holds the Map function to call on every element of the Float64Array array.
• thisArg: This parameter is optional and holds the value to use as this when executing mapFn.

Return Value: This method returns a new Float64Array instance.

Below examples illustrate the working of Float64Array.from() function in JavaScript:

Example 1: This example shows the basic working of the Float64Array.from() function in JavaScript.

// Create a Float64Array from a string like structure
let array = Float64Array.from('12345324354342354245342');

// Print the result
console.log(array);

Output: 

1, 2, 3, 4, 5, 3, 2, 4, 3, 5, 4, 3, 4, 2, 3, 5, 4, 2, 4, 5, 3, 4, 2

Example 2: This example shows the basic working of the Float64Array.from() function in JavaScript.

// Create a Float64Array from an array by
// multiplying 3999.99 to each number
// using function
let array = Float64Array.from(
    [432.3343, 13243.3243123, 1324232132.24551],
    z => z * 3999.99
);

// Print the result
console.log(array);

Output: 

1729332.8766569998, 52973164.81595687, 5296915286660.718