Javascript new syntax implementation

Question

Can anyone give me a direction on how to implement python like syntax of lists array[-1] using Babel in javascript? I mean how to implement negative indexes.

I know, but I am interesting in how to implement this as a new syntactic sugar using babel — FoxyJS, Jan 05 '21 at 17:21
That would be difficult to do with Babel - you could look for indexing with a negative value and try replacing that with the slice @ptothep suggests, but what if it turns out that wasn't an *array* being indexed into? There's no type information to leverage. Besides that a tutorial on writing a new Babel transform would be too broad for an SO question. — jonrsharpe, Jan 05 '21 at 17:22
Does this answer your question? [Python to JavaScript converter](https://stackoverflow.com/questions/22595989/python-to-javascript-converter) — Washington Guedes, Jan 05 '21 at 17:28

score 0 · Accepted Answer · answered Jan 05 '21 at 17:24

You could go with your own proxy implementation and then use it.

const letters = ['a', 'b', 'c', 'd', 'e'];
const proxy = new Proxy(letters, {
    get(target, prop) {
        if (!isNaN(prop)) {
            prop = parseInt(prop, 10);
            if (prop < 0) {
                prop += target.length;
            }
        }
        return target[prop];
    }
});
proxy[0]; // => 'a'
proxy[-1]; // => 'e'
proxy[-2]; // => 'd'

Please refer to this article on medium explaining in detail how to do this. I do not know of another way, perhaps there is a babel plugin that could help.

Javascript new syntax implementation

1 Answers1