Javascript String Property

Question

I came across some strange (legacy?) JS syntax this morning which boiled down to:
var example = "String".Property = "Value";

Before altering this code, I couldn't find a valid case for this implementation that I am aware of...

var example = "String".Property = "Value";
console.log(example);

"String".Property = "Value";
console.log("String".Property);
console.log(String.Property);

What actually happens to "String".Property in the first part of the above snippet, does it just get discarded immediately after being assigned ?

"String" is a literal string, and since you don't keep a reference to it it will be garbage collected whether you assign a property to it or not. — Jared Smith
– Jared Smith, Commented Sep 19, 2018 at 22:37

Pointy · Accepted Answer · 2018-09-19 22:37:05Z

3

String literals are string primitive values. When followed by a dot (.) operator, they are implicitly converted to a String instance.

The statement

var example = "String".Property = "Value";

is equivalent to

var example = "Value";

There is no point to the .Property reference.

Subsequently,

"String".Property = "Value";

has no net effect on the global environment, because the string constant "String" is converted to a String instance and the property is set, but then the object is discarded because it isn't assigned to anything.

Every use of the string constant "String" that results in an implicit object creation will cause a new unique object to be created.

answered Sep 19, 2018 at 22:37

Pointy

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3 Comments

Jared Smith Over a year ago

Indeed, typeof "foo" !== typeof new String("foo")

Dexygen Over a year ago

Multi-part answers should be closed as "Too Broad" and not answered.

Zze Over a year ago

Seeing obscure code like this always makes me question why it was implemented in the first place / what don't I know. Thanks for the clarity.

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