AngularJS - 为什么NG-绑定比前pressions更快？ [英] AngularJS - Why is ng-bind faster than expressions?
问题描述
From this question and this answer, it seems that using expressions will cause the value to be evaluated from scratch every time. But I've searched the documentation and tutorials, and I haven't found a reference for this statement.
在我的脑海里，都被包裹在一个 $表（）键，所以当 $消化（）循环运行时，它会看到里面是否值 NG-绑定或 {{}} 已经改变了。
In my mind, both are wrapped in a $watch() and so when the $digest() cycle runs it will see whether the value inside ng-bind or {{}} has changed.
在性能，这是为什么 NG-绑定比更好的{{}} 为已建议和哪来的参考？
On performance, why is ng-bind better than {{}} as has been suggested, and where's the reference?
推荐答案
这样的细节并不总是在文档中使用 - 你必须阅读源代码。我花了偷看，似乎（截至2014年11月24日），他们都在工作方式非常相似。都可以导致被实例化一个单一的指令改变数值需要（卷曲插补指令在飞行中产生的）。在
Details like this aren't always available in the documentation - you have to read the source. I took a peek and it seems that (as of 2014-11-24) they both work in a very similar way. Both cause a single directive to be instantiated to change the value when needed (the curly interpolation directive is generated on the fly).
这两个指令的评估所涉及的每 $消化就像一切除权pressions。主要的区别是，虽然纳克绑定没有做的价值的任何进一步的处理，与花括号，整个插文本在每个消化重新计算。基本上是一个字符串使用建 $插值 并与该previous值进行比较（这种情况 $的肠子内消化）。如果该值（无论是与平原值NG-绑定或花括号内插结果）没有变化也不方式将更新DOM。
Both directives evaluate the expressions involved on every $digest just like everything else. The main difference is that while ng-bind doesn't do any further processing on the value, with curlies, the entire interpolated text is recalculated on every digest. Essentially a string is built using $interpolate and that is compared with the previous value (this happens within the bowels of $digest). Neither way will update the DOM if the value (either the plain value with ng-bind or the interpolated result with curlies) hasn't changed.
要我对这个问题进行接受的答案是一个更令人信服的理由，使用 NG-绑定，即你可以用它来prevent角加载之前的模板标签可见闪光灯和编译它们，而不诉诸像NG-斗篷黑客。
To me the accepted answer on that question is a more compelling reason to use ng-bind, i.e. you can use it to prevent a visible flash of the template tags before Angular loads and compiles them, without resorting to hacks like ng-cloak.
根据变量也可能存在情况下，花插实际上是的更多的高性能。一种情况采用NG-绑定，而不是插时，我能想到的是要求你创建了很多，否则多余的＆LT的;跨度＆GT; 元素，并提示在秤另一个方向。插值前pression也导致整个字符串创建独立的使用多少变数单一观察者，而不是NG-绑定这对于每个实例创建一个观察者。
Depending on variables there may also be cases where curly interpolation is actually more performant. One situation I can think of is when using ng-bind instead of interpolation requires you to create a lot of otherwise redundant <span> elements, and that tips the scales in the other direction. An interpolation expression also causes a single watcher to be created for the entire string independent of how many variables you use, as opposed to ng-bind which creates one watcher for each instance.
但一如既往，不优化性能早，如果你这样做，轮廓找出哪些部分真正重要的。
But as always, don't optimize for performance early, and if you do, profile to find out which part really matters.
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