“这个"在地图函数 Reactjs 中未定义

本文介绍了“这个"在地图函数 Reactjs 中未定义的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在使用 Reactjs，编写菜单组件.

"使用严格";var React = require("react");var Menus = React.createClass({item_url:功能(项目，类别，文章){console.log('afdasfasfasdfasdf');var url='XXX';如果(项目.类型== 1){url = item.categoryId == null ?'javascript:void(0)' : path('buex_portal_browse_category', {slug: Categories[item.categoryId].slug});} else if (item.type == 2) {url = item.articleId == null ?'javascript:void(0)' : path('buex_portal_view_article', {slug: 文章[item.articleId].slug, id: item.articleId});} 别的 {url = item.url;}返回网址；},渲染:函数(){//console.log(this.props.menus);//正确返回var menuElements = this.props.menus.map(function (item1) {//返回错误:'cannot read property 'props' of undefined '返回 (<div><li><a href={this.item_url(item1, this.props.categories, this.props.articles )}>{item1.name}//上面同样的故障<i class="glyphicon glyphicon-chevron-right pull-right"></i></a><div class="子菜单"><div>{item1._children.map(函数(item2){返回 (<div><h4><a href={this.item_url(item2, this.props.categories, this.props.articles)}>{ item2.name }</a><ul>{item2._children.map(函数(item3){返回 (<div><li><a href={this.item_url(item3, this.props.categories, this.props.articles) }>{ item3.name }</a></li>

);})}

);})}

);});返回 (<div class="菜单"><ul class="nav nav-tabs nav-stacked">{菜单元素}

);}});

每当我在 map 函数中使用 'this' 时，它都是未定义的，但在它之外就没有问题.

错误:

无法读取未定义的属性‘props’"

谁来帮帮我！:((

解决方案

Array.prototype.map() 需要第二个参数来设置 this 在映射函数中引用的内容，因此将 this 作为保留当前上下文的第二个参数:

someList.map(function(item) {...}， 这个)

或者，您可以使用 ES6 箭头函数自动保留当前的 ​​this 上下文:

someList.map((item) => {...})

I'm working with Reactjs, writing a menu component.

"use strict"; var React = require("react"); var Menus = React.createClass({ item_url: function (item,categories,articles) { console.log('afdasfasfasdfasdf'); var url='XXX'; if (item.type == 1) { url = item.categoryId == null ? 'javascript:void(0)' : path('buex_portal_browse_category', {slug: categories[item.categoryId].slug}); } else if (item.type == 2) { url = item.articleId == null ? 'javascript:void(0)' : path('buex_portal_view_article', {slug: articles[item.articleId].slug, id: item.articleId}); } else { url = item.url; } return url; }, render: function () { // console.log(this.props.menus); // return correctly var menuElements = this.props.menus.map(function (item1) { // return fault : 'cannot read property 'props' of undefined ' return ( <div> <li> <a href={this.item_url(item1, this.props.categories, this.props.articles )}>{item1.name} // the same fault above <i class="glyphicon glyphicon-chevron-right pull-right"></i> </a> <div class="sub-menu"> <div> {item1._children.map(function (item2) { return ( <div> <h4> <a href={this.item_url(item2, this.props.categories, this.props.articles)}>{ item2.name }</a> </h4> <ul> {item2._children.map(function (item3) { return ( <div><li><a href={this.item_url(item3, this.props.categories, this.props.articles) }>{ item3.name }</a></li></div> ); })} </ul> </div> ); })} </div> </div> </li> </div> ); }); return ( <div class="menu"> <ul class="nav nav-tabs nav-stacked"> {menuElements} </ul> </div> ); } });

Whenever I use 'this' inside map function it is undefined, but outside it is no problem.

The error:

"Cannot read property 'props' of undefined"

Anybody help me ! :((

解决方案

Array.prototype.map() takes a second argument to set what this refers to in the mapping function, so pass this as the second argument to preserve the current context:

someList.map(function(item) { ... }, this)

Alternatively, you can use an ES6 arrow function to automatically preserve the current this context:

someList.map((item) => { ... })