6 ms·

Smooshes the evaluation of an object that can be many different shapes into an easy to understand operation. I think the HTTP response is a great example. It

• codedokode 8y ago
  Is not `switch` enough for this?
  • cevn 8y ago
    It's more concise than switch, as well as more powerful (can destructure objects). You can't set things equal to the result of a switch. I find the pattern very convenient. let day; switch (date) { case 1: day = "mon"; break; case 2: day = "tues"; break; default: day = "wed"; break; vs let day = match(date) { 1 => 'mon', 2 => 'tues' }
    • Zyst 8y ago
      In fairness I think that would look a bit more like this: const getDate = (date) => { switch (date) { case 1: return 'mon' case 2: return 'tues' default: return 'wed' } } let date = getDate(1) Which is, of course, still less terse. What I normally use when I have cases like this is an object-as-a-map. IE: const dates = { 1: 'mon', 2: 'tues' } let day = dates[3] || 'wed';
      • codedokode 8y ago
        By the way, I don't think it is a good idea to write a function as a constant. Please compare this function getDate(date) { .. } to this: const getDate = (date) => { ... } The first version is more readable. We instantly see that it is a function and in a second case it looks like a constant at first. Also without the equal and arrow sign it looks simpler.
        • Prefinem 8y ago
          Life is more fun with fat arrows sometimes new Promise(function (resolve, reject) { methodOne(data, function (error, response) { if (erorr) { reject(error); } else { resolve(response); } }) }) vs new Promise((resolve, reject) => methodOne(data, (error, response) => error ? reject(error) : resolve(response)));
          • goatlover 8y ago
            That one liner has a lot going on. The first one is easier to read.
            • mpfundstein 8y ago
              no
            • codedokode 8y ago
              Please also look at my idea how to rewrite the code for readability using `deferred` pattern: https://news.ycombinator.com/item?id=16933983 https://news.ycombinator.com/item?id=16933983
          • codedokode 8y ago
            Yes, there are cases when arrow functions are useful: when small functions are used inline, like this: var numbers = [1, 2, 3, 4].map(x => x * x); var bestUsers = users.filter(u => u.getRating() > 100); But for a case when you have a large non-anonymous function, `function` keyword suits better. You don't need to use `const` keyword just becase it is something trendy now. In your example, the code with arrow functions is smaller, but it is not more readable. Because there is no indentation, it is difficult to understand how code is nested. I cannot read that. It can be rewritten using `deferred` pattern: var deferred = new Deferred; methodOne(data, function (error, response) { if (erorr) { deferred.reject(error); } else { deferred.resolve(response); } }); return deferred.getPromise(); This way we can get rid of a callback in the Promise constructor. Please note that our code now looks sequential and we clearly see what happens after what. Asynchronous code is difficult to write and read; therefore we must put an extra effort to make it easier. In my opinion it is generally bad idea to nest more that 1-2 levels of functions inside each other.
  • zdragnar 8y ago
    From looking at the proposal, there are substantial differences. The biggest is that switch is an equality test on a single value, while pattern matching as proposed allows matching on multiple properties of an object, as well as conditional clauses. I need to look at it more closely, as some languages have matching be an expression, rather than a statement or block like the conventional switch. It doesn't add something that you can't already do- tcomb and other libraries offer functions that mimic it- but it changes the way you can express certain ideas without needing them, in a way that is already familiar from other languages. EDIT: yes, it does look like an expression, which means it can be used in many more places than a standard switch.
• 21 8y ago
  > Smooshes the evaluation I see what you did there...