Avoid unnecessary object allocation in ClassSet

[syranide]

react/src/vendor/stubs/cx.js

Line 36 in 8a47813

return Object.keys(classNames).filter(function(className) {

If we get rid of Object.keys we save one allocation for a potentially commonly used function (except for you guys running your internal transform). Yes no?

[twobit]

I would like to see a more flexible version of classSet. Something that allows for dynamic class names...

var myClassName = "bar";

classSetEx("foo", true, myClassName, true, "baz", false)

Here's my implementation:

  function classSetEx() {
    var args = Array.prototype.slice.call(arguments, 0),
        i,
        classes = {};

    for (i = 0; i < args.length; i += 2) {
      if (args[i]) {
        classes[args[i]] = args[i + 1];
      }
    }

    return React.addons.classSet(classes);
  }

[syranide]

@twobit You're free to implement your own version as you see fit, I think the idea behind classSet as it is, is that with fixed classNames they can be mangled/minified to use considerably less space.

[ssorallen]

@syranide You could use string concatenation instead of an array. String concatenation has gotten much faster in all browsers other than IE (faster in IE as well) according to a string concat vs. array join JSperf and some browser string concat implementation research on Stack Overflow.

function cx(classNames) {
  if (typeof classNames === 'object') {
    var clsNm;

    for (var key in classNames) {
      if (classNames.hasOwnProperty(key) && classNames[key]) {
        if (clsNm === undefined) {
          clsNm = key;
        } else {
          clsNm = clsNm + ' ' + key;
        }
      }
    }

    return clsNm;
  } else {
    return Array.prototype.join.call(arguments, ' ');
  }
}

[chenglou]

Closing this since we're deprecating classSet (#2910). The new alloc-free version lives at https://github.com/petehunt/react-classset