Within the realm of TypeScript, there exist two distinct variations of the "number" type. The first is denoted as lowercase number, whereas the second is represented in uppercase as Number. Attempting to display number results in a compiler error:
console.log(number); //-> error TS2693: 'number' only refers to a type
In contrast, viewing Number provides the standard function description:
console.log(Number); //-> [Function: Number]
This behavior is anticipated since Number serves as a pre-existing JavaScript constructor documented here. Nevertheless, the nature of number remains ambiguous.
From the error message, it appears that number does not embody a distinct value like
Number</code. Despite this, it is utilized in variable and function declarations as if it were a value:</p>
<pre class="lang-js"><code>var two: number = 2;
function sqr(x: number) { return x; }
In contrast, user-defined types such as classes appear as separate values (and exhibit the standard function description when printed). Adding complexity, Number can be employed in annotations similarly to number:
var two: Number = 2;
Similar scenarios arise with string and String, any and Object, and so forth.
Therefore, the inquiry stands: What exactly are number, string, etc in TypeScript, and how do they differ from the built-in constructors?