Curly braces vs. square braces

[mich...@chromium.org]

Is there a guideline for when to use curly vs. square braces, when the effect would be the same?

For example PRIMER.md uses curly braces for text content, but it's just a one-way binding:

<span>{{first}}</span>

Computed bindings are another example. PRIMER.md uses curly braces, which seems confusing because it's not really two-way binding:

<x-child some-property="{{getValue(otherThing)}}">

Finally in one-way downward binding (notify: true is not set on a property), using curly braces won't result in the host property being updated.

Are there any performance reasons to use one or the other? Or suggested style or forward-compatibility reasons?

[Arthur Evans]

There are no official guidelines. I think for the most part it's a style thing, and at the moment what you see in the docs may depend on who first wrote the example. There are two basic schools of thought:

School #1) Curly braces are "automatic" -- in almost all cases, they just do the right thing. Use 'em everywhere unless you specifically want to rule out the possibility of a two-way binding. (You'll see that a lot of the docs are written this way, partly for historical reasons -- 0.5 had only the curly brackets.)

School #2) Using square braces for all one-way bindings makes it easy to see the expected data flow. So use square brackets everywhere and only use curly brackets where you specifically want a two-way binding. (Most of the new elements follow this style.)

I'm not aware of big performance implications either way. I'd say pick your style and stick to it.

Cheers,

Arthur

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