Clourescript: converting array access

Question

Problem

I am trying to convert the following piece of code: https://github.com/mdn/webgl-examples/blob/gh-pages/tutorial/glUtils.js#L13-L15

The JavaScript code is:

Matrix.Translation = function (v)
{
 // ignore length 2 case for simplicty
 if (v.elements.length == 3) {
 var r = Matrix.I(4);
 r.elements[0][3] = v.elements[0];
 r.elements[1][3] = v.elements[1];
 r.elements[2][3] = v.elements[2];
 return r;
 }
 throw "Invalid length for Translation";
}

Now, I can rewrite it cljs as follows:

(defn translation [x y z]
 (let [r (. js/Matrix I 4)]
 r[0][3] = x ;; how do I write this?
 r[1][3] = y ;; how do I write this?
 r[2][3] = z ;; how do I write this?
 ))

Question

However, how do I write r[0][3] in cljs?

Answer 1

You can use aget and aset to work with Javascript arrays:

(def arr (array (array "a1" "a2") (array "b1" "b2") (array "c1" "c2")))

It creates following nested array:

#js [#js ["a1" "a2"] #js ["b1" "b2"] #js ["c1" "c2"]]

You can access nested elements with aget:

(aget arr 1 0)
;; => "b1"

And update with aset:

(aset arr 1 0 "newb1")

updates arr to:

#js [#js ["a1" "a2"] #js ["newb1" "b2"] #js ["c1" "c2"]]

You might want to take a look at other functions related to Javascript arrays: alength, array, make-array, array?.