如何在没有要映射的对象数组的情况下循环和渲染 React.js 中的元素? [英] How to loop and render elements in React.js without an array of objects to map?

问题描述

我正在尝试将 jQuery 组件转换为 React.js，我遇到的困难之一是基于 for 循环渲染 n 个元素.

我理解这是不可能的，或推荐的，并且如果模型中存在数组，则使用 map 完全有意义.那很好，但是当您没有数组时怎么办?取而代之的是，您的数值等于要呈现的给定数量的元素，那么您应该怎么做?

这是我的示例，我想根据元素的层次级别为元素添加任意数量的跨度标记作为前缀.所以在第 3 级，我希望在文本元素之前有 3 个 span 标签.

在 JavaScript 中:

for (var i = 0; i 

我似乎无法理解这个，或者任何类似于在 JSX React.js 组件中工作的东西.相反，我必须执行以下操作，首先构建一个正确长度的临时数组，然后循环该数组.

React.js

render: function() {var tmp = [];for (var i = 0; i < this.props.level; i++) {tmp.push(i);}var indents = tmp.map(function (i) {返回 (<span className='indent'></span>);});返回 (...{缩进}一些文本值"...);}

这肯定不是最好的，还是唯一的方法?我错过了什么?

解决方案

更新:从 React > 0.16 起

Render 方法不一定必须返回单个元素.也可以返回一个数组.

var indents = [];for (var i = 0; i < this.props.level; i++) {indents.push(<span className='indent' key={i}></span>);}返回缩进；

或

return this.props.level.map((item, index) => (<span className="indent" key={index}>{指数}</span>));

此处的文档解释了 JSX 子项

<小时>

旧:

你可以用一个循环代替

var indents = [];for (var i = 0; i < this.props.level; i++) {indents.push(<span className='indent' key={i}></span>);}返回 (<div>{缩进}一些文本值"

);

您也可以使用 .map 和花哨的 es6

返回(<div>{this.props.level.map((item, index) => (<span className='indent' key={index}/>))}一些文本值"

);

此外，您必须将返回值包装在容器中.我在上面的例子中使用了 div

正如文档所说这里

<块引用>

目前，在一个组件的渲染中，你只能返回一个节点；例如，如果您有一个要返回的 div 列表，则必须将组件包装在 div、span 或任何其他组件中.

I'm trying to convert a jQuery component to React.js and one of the things I'm having difficulty with is rendering n number of elements based on a for loop.

I understand this is not possible, or recommended and that where an array exists in the model it makes complete sense to use map. That's fine, but what about when you do not have an array? Instead you have numeric value which equates to a given number of elements to render, then what should you do?

Here's my example, I want to prefix a element with an arbitrary number of span tags based on it's hierarchical level. So at level 3, I want 3 span tags before the text element.

In javascript:

for (var i = 0; i < level; i++) {
    $el.append('<span class="indent"></span>');
}
$el.append('Some text value');

I can't seem to get this, or anything similar to work in a JSX React.js component. Instead I had to do the following, first building a temp array to the correct length and then looping the array.

React.js

render: function() {
  var tmp = [];
  for (var i = 0; i < this.props.level; i++) {
    tmp.push(i);
  }
  var indents = tmp.map(function (i) {
    return (
      <span className='indent'></span>
    );
  });

  return (
    ...
    {indents}
    "Some text value"
    ...
  );
}

Surely this can't be the best, or only way to achieve this? What am I missing?

解决方案

Updated: As of React > 0.16

Render method does not necessarily have to return a single element. An array can also be returned.

var indents = [];
for (var i = 0; i < this.props.level; i++) {
  indents.push(<span className='indent' key={i}></span>);
}
return indents;

OR

return this.props.level.map((item, index) => (
    <span className="indent" key={index}>
        {index}
    </span>
));

Docs here explaining about JSX children

---

OLD:

You can use one loop instead

var indents = [];
for (var i = 0; i < this.props.level; i++) {
  indents.push(<span className='indent' key={i}></span>);
}
return (
   <div>
    {indents}
    "Some text value"
   </div>
);

You can also use .map and fancy es6

return (
   <div>
    {this.props.level.map((item, index) => (
       <span className='indent' key={index} />
    ))}
    "Some text value"
   </div>
);

Also, you have to wrap the return value in a container. I used div in the above example

As the docs say here

Currently, in a component's render, you can only return one node; if you have, say, a list of divs to return, you must wrap your components within a div, span or any other component.

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