Calling JavaScript object property as a constructor from ClojureScript

Question

I am using a JavaScript library that exposes a constructor as a property of a global object.

In JavaScript, I can call the constructor like this.

var thing = new Library.Thing();

How do I call the constructor in ClojureScript? None of these work.

; These all cause compiler errors
(new (.-Thing js/Library)) ; First arg to new must be a symbol
(new (.Thing js/Library))
(new .-Thing js/Library)
(new .Thing js/Library)
(new js/Library/Thing)     ; Invalid token: js/Library/Thing

; These all compile to different JS than I am looking for
((.-Thing js/Library).) ; Library.Thing.call(null, _SLASH_);
((.Thing js/Library).)  ; Library.Thing().call(null, _SLASH_);

It works fine if I use js* but that's cheating, right?

(js* "new Library.Thing()")

What is the proper way to call a constructor function that is a property of another object?

tangrammer · Accepted Answer · 2013-10-23 08:23:13Z

11

If you look at http://himera.herokuapp.com/synonym.html you can find the specific syntax to instantiate objets in clojurescript.

I wrote this js mock library based in this documentation to make a test:

function Person(name) {
this.name = name;
}

Person.prototype.greet = function() {
return "Hello, " + this.name;
};


var f={
"hola":"hola juan",

Person:Person

};

var person=new f.Person("Juan");
alert(person.greet());

Then from clojurescript you have to use the dot syntax (but prefixing with "js/" your js global type):

(let [Person (.-Person js/f)
        juan (Person. "Juan")
        ]
    (.log js/console  (.greet juan)))

I don't mention in this answer the :externs property of your cljsbuild compilation beacuse I understand that you are including your js script library directly in your html head document. So, if this line works for you (js* "new Library.Thing()") it'll mean that the js library is available from the cljs-js-compiled.
Anyway, I left an "alert" in the js mock library to check that the file is correctly loaded

I hope it works for you
Juan

edited Oct 23, 2013 at 8:23

answered Oct 23, 2013 at 8:02

tangrammer

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2 Comments

Josh Headapohl Over a year ago

So in other words, if I bind the constructor to a local first, I can call it. (let [Thing (.-Thing js/Library)] (new Thing)) works fine, as does (let [Thing (.-Thing js/Library)] (Thing.)).You are correct about the script being included directly in the document.

tangrammer Over a year ago

Hi Josh, you are right about the local constructor binding. It's a very curious behavior the dot js constructor ".". Just realizing that you can invoke normal functions with this "." (defn -log [message] (.log js/console message) ) (-log. "Hello Josh")

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