Question

What is the difference between parseInt(string) and Number(string) in JavaScript has been asked previously.

But the answers basically focused on the radix and the ability of parseInt to take a string like "123htg" and turn it into 123.

What I am asking here is if there is any big difference between the returns of Number(...) and parseFloat(...) when you pass it an actual number string with no radix at all.

Answer 1

No. Both will result in the internal ToNumber(string) function being called.

From ES5 section 15.7.1 (The Number Constructor Called as a Function):

When Number is called as a function rather than as a constructor, it performs a type conversion…

Returns a Number value (not a Number object) computed by ToNumber(value) if value was supplied, else returns +0.

From ES5 section 15.1.2.3 (parseFloat (string)):

…
If neither trimmedString nor any prefix of trimmedString satisfies the syntax of a StrDecimalLiteral (see 9.3.1)
…

And 9.3.1 is the section titled “ToNumber Applied to the String Type”, which is what the first quote is referring to when it says ToNumber(value).

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Update (see comments)

By calling the Number constructor with the new operator, you will get an instance of the Number object, rather than a numeric literal. For example:

typeof new Number(10); //object
typeof Number(10); //number

This is defined in section 15.7.2 (The Number Constructor):

When Number is called as part of a new expression it is a constructor: it initialises the newly created object.