setting string properties in js

Question

Is it possible to somehow attach additional properties to strings in js? I am picturing something along the lines of

var s = "Hello World";
s.x = 'bar';

console.log(s.x);

Unfortunately, s.x is undefined after the assignment.

I know this question seems a little of. Why would you want to attach additional properties to a string after all? In my case the reasoning is as following: I am using a (questionably designed) library, which provides a function to create an xhr request given an url. The url is then passed to a callback function with the result.

Picture the library (xhr-function) similar to:

var xhr = function(url, cb){
    $.ajax({
        url: url,
        success: function(data){
            // do library stuff

            // my code goes here
        }
    })
}

Part of the framework is, that the callback function is not passed as a function but copied into the success handler body. This way I am able to access the url parameter in the my code goes here-section.

Now in my cb-handler, I need additional data other than just the url. Is there a way to hack this on to the url parameter? Unfortunately I can't change the library :(

I was planning to do something like:

var xhr = function(url, cb){
    $.ajax({
        url: url,
        success: function(data){
            // do library stuff

            // my code goes here
            // access url.foo
        }
    })
}

var url = 'https://example.com'
url.foo = 'bar'
xhr(url);

Strings are one of the primitive types, ie. not objects so you can't attach properties to them like this. — jakeehoffmann
– jakeehoffmann, Commented Mar 30, 2017 at 9:29
to attach props to string, use concat or join. str.concat('?bar=a&baz=c') — FrankCamara
– FrankCamara, Commented Mar 30, 2017 at 9:29
you'd have s as an object rather than a string or a function (otherwise you're mutating the expected behaviour of the string and that's unexpected and somewhat poor design) — Denis Tsoi
– Denis Tsoi, Commented Mar 30, 2017 at 9:29
also this question is a possible duplicate of Why can't I add properties to a string object in javascript? — Denis Tsoi
– Denis Tsoi, Commented Mar 30, 2017 at 9:30
Possible duplicate of Why can't I add properties to a string object in javascript? — niklasfi
– niklasfi, Commented Mar 30, 2017 at 9:49

Community · Accepted Answer · 2017-05-23 11:54:09Z

1

according to skilldrick on duplicate SO Question why can i add new attr to string obj

var s = new String("hello world!");
s.x = 5;
console.log(s.x); //5
console.log(s); //[object Object]
console.log(s.toString()); //hello world!

I still wouldn't advice it tho; (not exactly intuitive behaviour)

edited May 23, 2017 at 11:54

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answered Mar 30, 2017 at 9:35

Denis Tsoi

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