The following calls returns value of 0:
var n1 = Number() // n1 === 0 is true
var n2 = Number("") // n2 === 0 is true
var n3 = Number(null) // n3 === 0 is true
I tried above in Google Chrome Version 64.0.3282.119
But, is this behavior well-defined? I'm not sure if it behaves the same way in other browsers.
From the ECMAScript specification
For string-to-number conversion, there is added information in the next section: https://www.ecma-international.org/ecma-262/8.0/index.html#sec-tonumber-applied-to-the-string-type
Yes this is an expected behavior on all the browsers.
Any non executable value passed to constructor of Number will return 0.
var num1 = Number();
var num2 = Number("");
var num3 = Number(false);
var num4 = Number(null);
// here num1, num2, num3 and num4 will be 0 as undefined, empty string, false and null are non-executable values.
If you pass executable non-number value to constructor of Number, it will return NaN
var num5 = Number("abc");
var num6 = Number({});
var num7 = Number([]);
// num5, num6 and num7 will be NaN as non-empty string, any object and any array are executable but Not a number values.
When no argument is provided Number() will always return 0 and if the argument is illegale so Number() will return NaN
ToNumber()internal operation description in the language spec.