更新“占位符"使用基因剔除的属性 [英] updating "placeholder" attribute using knockout

问题描述

我有一个表单，其中的某些字段使用淘汰表(版本2.1.0)获取一些数据. 例如，要更新输入的值"字段:

I have a form with some fields getting some data using knockout.js (ver. 2.1.0). For example, to update the "value" field of an input I put:

<input type="text"  name="contrasena" id="login-user" value="" placeholder="" data-bind="value: user">

我有一个JSON来存储我想用于"pass"关键字的值，并且它可以正常工作.

I have a JSON to store the value a I want to use for "pass" keyword, and it works correctly.

我尝试使用相同的方法设置占位符"属性，但无效:

I tried to set "placeholder" attribute using the same method, but it doesn't works:

<input type="text"  name="contrasena" id="login-user" placeholder="" data-bind="placeholder: user">

我试图修改基于基于"ko.bindingHandlers ['value']"的"ko.bindingHandlers ['placeholder']"功能的knockout.js文件(修改"ko.jsonExpressionRewriting"中的"placeholder"而不是"value") .writeValueToProperty"函数)，但无法正常运行，它将信息置于值"属性中，而不是占位符"中.

I tried to modify knockout.js file adding "ko.bindingHandlers['placeholder']" function based on "ko.bindingHandlers['value']" (modifying "placeholder" instead of "value" in "ko.jsonExpressionRewriting.writeValueToProperty" function), but it doesn't work correctly, it puts the information in "value" attribute instead of "placeholder".

有人知道解决这个问题的方法吗?

Anyone knows the way to solve this?

非常感谢您！

推荐答案

如果要使用data-bind="placeholder: user"，则可以创建

If you want to use data-bind="placeholder: user", you can create a custom-binding in your js code.

使用ko.bindingHandlers['placeholder']的位置正确，但是您无需编辑基因敲除js文件-实际上，这是一种不好的做法..

You were on the right path using ko.bindingHandlers['placeholder'] but you don't need to edit the knockout.js file -- in fact, that is bad practice.

这将需要一个非常基本的自定义绑定:

This would require a very basic custom-binding:

ko.bindingHandlers.placeholder = {
    init: function (element, valueAccessor, allBindingsAccessor) {
        var underlyingObservable = valueAccessor();
        ko.applyBindingsToNode(element, { attr: { placeholder: underlyingObservable } } );
    }
};

有关自定义绑定的指南，请参见这里

For a guide on custom-bindings, see here

尽管淘汰赛本身就很吸引人，但这要少得多.它从视图中删除了有关如何将占位符应用于元素的知识.

Although Knockout is itself inherently obtrusive, this is slightly less. It removes the knowledge of how the placeholder is applied to the element from the view.

实际上，如果将来您想应用某种jQuery插件在不支持placeholder属性的浏览器中显示占位符，那么这里就是初始化插件的位置(init:)- -在这种情况下，您还需要update:函数.

In fact, if in the future you wanted to apply some sort of jQuery plugin to show placeholders in browsers which don't support the placeholder attribute, this would be the place (init:) to initialise the plugin -- you would also need an update: function in that case.

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