Transpiling R to JavaScript

To be productive developing JavaScript application in R, it is helpful to know some of the correspondence between the R and JavaScript syntax. This will not only help you debug your code better, but also make it easier to read the documentation of JavaScript libraries.

The three most common conversions

1. list maps to a JavaScript Object

   • list(x = 1, y = 1) becomes {x: 1, y: 1}

   Most JavaScript libraries store and manipulate data using JavaScript Object.

2. c gives a JavaScript Array with copy-by-value semantics and without nesting

   • Array(1, 2, Array(3, 4)) becomes [1, 2, [3, 4]];
   • c(1,2, c(3,4)) gives [1, 2, 3, 4];

   Some JavaScript libraries may expect nested Array as input, in which case one has to use Array instead of c.

3. $ and :: in R maps to . in JavaScript

   • In words, objects and namespaces in R (syntactically) map to objects in JavaScript.
   • It is common to see JavaScript libraries organise their functions with an object. For instance, functions in mathjs are stored in the object called math and one calls a function fun_1 by math.fun_1. To do that in R, simply load the library using the #! header, then call the function by the name math::fun_1 or math$fun_1.