AngularJS条件语句中的HTML属性 [英] AngularJS conditionals in HTML Attribute

问题描述

你将如何改变基于模型的 HTML 属性？

How would you change an html attribute based on the model?

我想基于阵列的长度来改变输入的占位符文本：

I'm trying to change an input's placeholder text based on a length of an array:

<input placeholder="{{todos.length ? 'Insert todo' : 'Insert your first todo'}}" />

但是，这似乎并没有工作...

But that doesn't seem to work...

JS斌code例如。

推荐答案

有关其他人谁遇到这样（像我刚刚通过谷歌所做的那样），它看起来像角最近增加了对前pressions三元运营商支持。我只是用它成功地在1.2.16动态更新提示（标题）属性。它似乎已经首次出现了1.2.17的文档中，虽然他们仍普遍鼓励使用：

For anyone else who comes across this (like I just did via Google), it looks like Angular recently added support for the ternary operator in expressions. I just used it successfully in 1.2.16 to dynamically update a tooltip (title) attribute. It seems to have first appeared in the documentation for 1.2.17, although they still generally discourage its use:

从：<一href=\"https://$c$c.angularjs.org/1.2.17/docs/guide/ex$p$pssion#no-control-flow-statements\">AngularJS:开发人员指南：防爆pressions

除了三元运算符（A B：C），你可以不写在一个前pression控制流的语句。这背后的原因是核心的角理念使应用程序逻辑应该在控制器，而不是意见。如果你需要一个真正的条件，循环，或从视图前pression扔，委托给一个JavaScript方法来代替。

Apart from the ternary operator (a ? b : c), you cannot write a control flow statement in an expression. The reason behind this is core to the Angular philosophy that application logic should be in controllers, not the views. If you need a real conditional, loop, or to throw from a view expression, delegate to a JavaScript method instead.

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