Show HN: I built an extension of JavaScript in a day | Hacker News Reader

Show HN: I built an extension of JavaScript in a day

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26 pointschmod77517 comments

1. Instead of implementing it in vanilla JavaScript, consider creating a Sweet.js macros (or series of macros), so it can be used with other flavors of JS as well (e.g. JSX, etc)

2. On the async functions – what happens if you put an async function inside a conditional? This is effectively solved by ES6's yield + co or an equivalent.

3. A nitpick, but, is there a way to create static functions on classes? E.g. Car.x instead of Car.prototype.x?

1. uh... oh

2. I'm not sure if I understand your correctly, but it should work if you wrap it in (). I actually have that very same example in 'broken.js' [0]

3. Sure. As you can write normal JavaScript, just use:

   Car.x = (arg){
       //etc
   }

The ':' operator is supposed to be a shortcut for X.prototype.Y

[0]: https://github.com/binlain/designtojs/blob/master/test/broke...

Sorry, should have clarified on 2. As an expansion of one of the examples given:

    loadAndPrintFile: (contents) {
       if (!contents) {
         fs.readFile() -> (error!, contents)
       }
       console.log(contents);
    }

i.e., expected behavior would be as if readFile was not an async function.

I'm asking because I built something similar (though it only worked with promises, not general async functions), and I'm curious to compare approaches :-) - mine is a sweet.js macro: http://pastie.org/9410315 (uses https://github.com/petkaantonov/bluebird and https://github.com/BranchMetrics/promise-accum). The basic syntax would be:

    task {
      item1 <- LoadItem(1);
      item2 <- LoadItem(item1.foreign_key);
      ret <- DoSomethingWithItems(item1, item2);
    }

The JavaScript result of your example looks like this:

(again, beautified because DesignToJS crams everything in one line to preserve the line numbers of your actual code):

  function loadAndPrintFile(contents) {
    if (!contents) {
      fs.readFile(function(error, contents){
        if(error !== null && error !== undefined){
          return error;
        }
      });
    }
    console.log(contents);
  }

If you omit the function body, it will only expand to the end of the current logical 'context' (or whatever it's called)

I'd suggest writing it like this in DesignToJS:

  loadAndPrintFile: (contents! console.log) {
    fs.readFile() -> (error!, contents! console.log)
  }

Result looks like this:

  function loadAndPrintFile(contents) {
      if(contents !== null && contents !== undefined){
          return console.log(contents);
      }
      fs.readFile(function(error, contents){
          if(error !== null && error !== undefined){
              return error;
          }
          if(contents !== null && contents !== undefined){
              return console.log(contents);
          }
      });
  }

Edit: I just submitted a patch that avoids unnecessary binding of 'this' if 'this' is not actually used.

In Javascript (contents !== null && contents !== undefined) is equivalent to (contents != null).

Now that is good to know, thank you. I'll make that change asap.

Ah, very interesting use of the ! operator.

You'll have a hard time fighting GitHub classifying `.djs` as DogeScript....

Nevertheless, good luck with the project and everything.

Looks like the readme example doesn't work. I didn't compile the djs sayHello function to verify it matches the given javascript, but running sayHello("nyc") spits out

  Hello to undefined, nyc
  You didn't tell me your age

When I'd assume you wanted

  Hello to nyc, Tim
  You didn't tell me your age

The first argument is the name, the second is city.

If you give a third, the second will be your age and the third your city.

Example:

   sayHello('Andreas', 'Berlin')
   sayHello('Andreas', 21, 'Berlin')

Firstly, congratulations on making something useful in one day. Great job. I skimmed over the documentation/examples and this is excellent.

By the way, `typeof X === 'undefined'` doesn't need to be used for variable names that exist such as arguments, you can use X == undefined without opportunity for failure.

Technically, all edge cases considered, `typeof` is the only fool-proof check, since you can't override the string constant `'undefined'` but the `undefined` identifier is fair game.

Here is one such edge case:

    (function () {
      var undefined = true;
      return (function foo(x) {
        return x === undefined;
      }());
    }()); // false

Language pedantry aside, browsers these days will freeze `window.undefined` so you'd have to shoot yourself in your own scope ;)

if you're that determined to shoot yourself in the foot you might as well rebind valueOf

Thank you! I'll fix it asap.

This looks cool but I think your syntax clashes with JS's standard LabeledStatement

Good thinking, but I already do detect and handle that case correctly.

There's a test case in 'test/namedThings.(d)js'

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