The conditionals are correct, but a little hard to follow. Do you think this would be any better?

```javascript
if (isInputSupported) {
  if (topLevelType !== topLevelTypes.topInput) {
    return;
  }
  // ...
} else {
  if (topLevelType === topLevelTypes.topFocus) {
    // ...
    return;
  }
  if (topLevelType === topLevelTypes.topBlur) {
    // ...
    return;
  }
  if (topLevelType !== topLevelTypes.topSelectionChange &&
      topLevelType !== topLevelTypes.topKeyUp &&
      topLevelType !== topLevelTypes.topKeyDown) {
    return;
  }
  // ...
}
```

Or better yet...

```javascript
var extractEvents;
if (isInputSupported) {
  extractEvents = function() {
    // Modern browsers...
  };
} else {
  extractEvents = function() {
    // IE<10...
  };
}
```