Question

我正在遵循本教程

https://nickymeuleman.netlify.com/blog/gatsby-pagination#navigate-to-previousnext-page

一切正常，但是我无法在类中添加const。我正在使用VSC对网站进行编码，但似乎并不喜欢它。

这是我要在其中放置const的类。由于我是React的新手，因此在不使用插件的情况下找到解决方案就迷失了自己。

export default class PostList extends React.Component {
    render() {
        const posts = this.props.data.allMarkdownRemark.edges
        return (
            <Layout>
                <Head title="Posts" />
                <div className={layoutStyles.pageHeader}>
                    <h2>Posts</h2>
                    <span>Just my ramberlings</span>
                </div>
                {posts.map(({ node }) => {
                    const title = node.frontmatter.title || node.fields.slug
                    return (
                        <div className={postPageStyles.postItem}>
                            <div className={postPageStyles.postItemTitle}>
                                <h2>{title}</h2>
                                <span>Posted on {node.frontmatter.date}</span>
                            </div>
                            <div>
                                <p>{node.excerpt}</p>
                                <Link to={`${node.fields.slug}`}>
                                    <span>Continue Reading</span>
                                    <span role="img"> ??</span>
                                </Link>
                            </div>
                        </div>
                    )
                })}
            </Layout>
        )
    }
}

Answer 1

此功能是否起作用？请注意，您不再访问this.props.data，而可以直接访问已解构的data变量。

const PostList = ({data}) => {
    const posts = data.allMarkdownRemark.edges
    return (
      <Layout>
        <Head title="Posts" />
        <div className={layoutStyles.pageHeader}>
          <h2>Posts</h2>
          <span>Just my ramberlings</span>
        </div>
        {posts.map(({ node }) => {
          const title = node.frontmatter.title || node.fields.slug
          return (
            <div className={postPageStyles.postItem} key={node.fields.slug}>
              <div className={postPageStyles.postItemTitle}>
                <h2>{title}</h2>
                <span>Posted on {node.frontmatter.date}</span>
              </div>
              <div>
                <p>{node.excerpt}</p>
                <Link to={`${node.fields.slug}`}>
                  <span>Continue Reading</span>
                  <span role="img"> ??</span>
                </Link>
              </div>
            </div>
          )
        })}
      </Layout>
    )
  }

  export default PostList

export const query = graphql`{...}`

Answer 2

您实际上不能在“就这样”的类中使用const：

class App extends React.Component {
  const a = 2 // will throw a syntax error
  render(){
   return <div>Hello World</div>
  }

您可以做的就是不使用const将该变量声明为类字段：

class App extends React.Component {
   a = "john";

  render(){
   //now you can access a via `this`
   return <div>{`Hello ${this.a}`}</div>
  }

或者如果您不需要它以某种方式“绑定”到您的组件，则可以在类外声明它。

const a = "john"

class App extends React.Component {
  render(){
   //you can simply access `a` 
   return <div>{`Hello ${a}`}</div>
  }

Answer 3

我设法解决了这个问题。经过大量的搜索。

const PostList = props => {
    const { currentPage, numPages } = props.pageContext
    const isFirst = currentPage === 1
    const isLast = currentPage === numPages
    const prevPage = currentPage - 1 === 1 ? '/' : (currentPage - 1).toString()
    const nextPage = (currentPage + 1).toString()

    const posts = props.data.allMarkdownRemark.edges

    return (
        <Layout>
            <Head title="Posts" />
            <div className={layoutStyles.pageHeader}>
                <h2>Posts</h2>
                <span>Just my ramberlings</span>
            </div>
            {posts.map(({ node }) => {
                const title = node.frontmatter.title || node.fields.slug
                return (
                    <div className={postPageStyles.postItem}>
                        <div className={postPageStyles.postItemTitle}>
                            <h2>{title}</h2>
                            <span>Posted on {node.frontmatter.data}</span>
                        </div>
                        <div>
                            <p>{node.excerpt}</p>
                            <Link to={`${node.fields.slug}`}>
                                <span>Continue Reading</span>
                                <span role="img"> ??</span>
                            </Link>
                        </div>
                    </div>
                )
            })}

            {!isFirst && (
                <Link to={prevPage} rel="prev">
                    ← Previous Page
                </Link>
            )}
            {!isLast && (
                <Link to={nextPage} rel="next">
                    Next Page →
                </Link>
            )}

            {Array.from({ length: numPages }, (_, i) => (
                <Link
                    key={`pagination-number${i + 1}`}
                    to={`posts/${i === 0 ? '' : i + 1}`}
                >
                    {i + 1}
                </Link>
            ))}
        </Layout>
    )
}

export default PostList

要使用consts，我必须进行更改

const PostList = ({ data }) => {
    const posts = data.allMarkdownRemark.edges
    ...

到

const PostList = props => {

    const posts = props.data.allMarkdownRemark.edges

然后允许我使用const { currentPage, numPages } = props.pageContext

无法在React中的类中使用const

3 个答案: