javascript - Symbol.for(string) in ECMAScript 6

Question

It took me a while but I finally figured out what the purpose of symbols in ECMAScript 6 is: avoiding name collision when attaching properties to shared objects - HTML elements e.g. (In case you're stuck on the same question, I recommend this article.)

But then I stumbled upon Symbol.for(). Apparently ECMAScript 6 will maintain a global symbol registry which you can query with this function by providing the symbol description. Come again? If I use symbols to avoid name collisions, why would I want code other than my own to use them? (*) And how would I avoid name collisions in that global registry? Sharing of symbols seems to completely subvert the concept and a global registry doubly so.

(*) Yes, I know symbols aren't truly private, but that's besides the point.

Answer 1

If you don't want your symbols to be available in GlobalSymbolRegistry, just don't use Symbol.for.

Only use it if you want to allow other codes to use your symbol.

In the following example, I create a symbol to store data in DOM elements. And I may want every other code (e.g. internal raw uncompiled handlers) to read that data. So I make the symbol globally available.

var sym = Symbol.for('storeDataInDOM');
document.querySelector('button')[sym] = 'Hello, world!';

<button onclick="alert(this[Symbol.for('storeDataInDOM')])">Click me</button>