警告：React.createElement：类型不应为空或未定义

Question

期望下面的代码将无序列表及其子 <"li" /> 节点附加到 document.body，<"ul" /> 没问题，但没有任何子节点并且在控制台：

React.createElement: type should not be null or undefined. It should be a string (for DOM elements) or a ReactClass (for composite components).

(React.js ver.0.13)

var ListView = React.createClass({
    render: function() {
        var items = this.props.data.map(function(item) {
            return ItemDelegate({key:item.id, data:item.id});
        }.bind(this));
        return (React.createElement('ul', null, items));
    }
});

var ItemDelegate = React.createFactory(ListViewChildren);

var ListViewChildren = React.createClass({
    render: function(){
        return (React.createElement('li', {key: this.props.key, data: this.props.data}));
    }
});

var Wrapper = React.createClass({
    render: function() {
        return (React.createElement(ListView, {data: [/*some data*/]}));
    }
});

React.render(React.createElement(Wrapper), document.body);

它是什么 type 并且必须在何处声明规定的 type？我想在某个地方对这个概念有完全的误解，但是在哪里呢？

Answer 1

警告来自

var ItemDelegate = React.createFactory(ListViewChildren);

ListViewChildren 定义如下，因此 React 无法创建工厂。

只要移动上面的var ListViewChildren = ...，警告就会消失。

您在 ListView class 中也有问题：您的 items 应该是 children 而不是 props:

// items as props (2nd arg): won't work, html elements don't have props :)
return (React.createElement('ul', items));
// items as children (3rd arg) should work better
return (React.createElement('ul', null, items));

完整代码：http://jsfiddle.net/Lmb7t9pv/2/

警告：React.createElement：类型不应为空或未定义

Warning: React.createElement: type should not be null or undefined

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