new String('foo') returns wrong type

[rwaldron]

While writing tests for #283 there were failures caused by new String("foo") return value being a string.

The correct return is a String object:

var o = new String('foo');
var s = 'foo';

console.log(typeof o === 'object');
console.log(o instanceof String);

console.log(typeof s === 'string');
console.log((s instanceof String) === false);

The expected result is true for all of the above, the actual results are:

false
true
true
false

[gfwilliams]

This will be the same issue as #187 - I don't suppose you know whether there's a standard way to implement the 'boxed' types? (whether they have some internal field called value or suchlike)

[rwaldron]

Indeed, there is a "hidden" internal property called [[PrimitiveValue]] where the primitive string is stored. This value is returned by the string's valueOf and toString methods

[gfwilliams]

Thanks!

[bartmichu]

I'm not sure, but possibly it's the same issue here?

var arr = new Array(2);

typeof arr;  //returns "object"

arr instanceof(Object);  //returns false, expected true

function f() {console.log("test")}
f instanceof(Object)  //returns false, expected true

[rwaldron]

@zigrin no, this is simply due to the lack of an actual ECMAScript object prototype chain implementation

[gfwilliams]

Just a note on this:

• String("Foo") just returns "Foo"
• new String("Foo") returns a boxed string of "Foo"
• function S() {return"Foo"};S() returns "Foo" (as expected)
• function S() {return"Foo"};new S() returns {} (so it's not like you can make new box stuff. The String constructor function needs to be aware of whether it's being called as a constructor or not)

[MaBecker]

As is works as designed, why not close it.

[gfwilliams]

My note above is what should happen. What does happen is actually different (everything stays unboxed).

The issue is that it's not as easy as just making the String constructor return a 'boxed' string - since when it's not called as a constructor it does something different, which isn't something that's supported in Espruino at the moment.

I guess a fix might be for new itself to decide whether it was called on String/Number/Boolean/etc and to automatically box those values.