如何在按鈕上運行警報單擊React.js

Question

我一直在運行一個反應文件上傳教程，並希望添加它。 我試圖這樣做，當用戶點擊上傳消息時，瀏覽器會提示他們說“你的文件正在上傳”我不是任何方式的前端開發者所以請原諒我，如果這個問題超級高興。 出於某種原因，當我使用此代碼時，如果您導航到網頁，該函數中的代碼將運行一次，然后再次單擊。 我的用途是只運行點擊，任何想法我做錯了什么？

import React, { Component } from 'react'
import { Alert } from 'react-alert'

class Main extends React.Component {
  constructor(props) {
    super(props);

    this.state = {
      imageURL: '',
    };

    this.handleUploadImage = this.handleUploadImage.bind(this);
  }

  handleUploadImage(ev) {
    ev.preventDefault();

    const data = new FormData();
    data.append('file', this.uploadInput.files[0]);
    data.append('filename', this.fileName.value);

    fetch('http://localhost:8000/upload', {
      method: 'POST',
      body: data,
    }).then((response) => {
      response.json().then((body) => {
        this.setState({ imageURL: `http://localhost:8000/${body.file}` });
      });
    });
  }

  render() {
    return (
      <form onSubmit={this.handleUploadImage}>
        <div>
          <input ref={(ref) => { this.uploadInput = ref; }} type="file" />
        </div>
        <div>
          <input ref={(ref) => { this.fileName = ref; }} type="text" placeholder="Enter the desired name of file" />
        </div>
        <br />
        <div>
          <button onclick="myFunction()">Upload</button>
              <script>
              function myFunction() {
                  alert("Your file is being uploaded!")
              }
              </script>

        </div>
        <img src={this.state.imageURL} alt="img" />
      </form>
    );
  }
}

export default Main;

Answer 1

為什么不在handleUploadImage函數開頭移動警報？

handleUploadImage(ev) {
    alert("Your file is being uploaded!")
    ....
}

而不是

<div>
  <button onclick="myFunction()">Upload</button>
      <script>
      function myFunction() {
          alert("Your file is being uploaded!")
      }
      </script>

</div>

你將會有

<div>
  <button type="submit">Upload</button>
</div>

Answer 2

對於任何好奇的人，這是我收到的幫助后的最終代碼。

import React, { Component } from 'react'
import { Alert } from 'react-alert'

class Main extends React.Component {


  constructor(props) {
    super(props);

    this.state = {
      imageURL: '',
    };

    this.handleUploadImage = this.handleUploadImage.bind(this);
  }

  handleUploadImage(ev) {
    alert("Your file is being uploaded!")
    ev.preventDefault();

    const data = new FormData();
    data.append('file', this.uploadInput.files[0]);
    data.append('filename', this.fileName.value);

    fetch('http://localhost:8000/upload', {
      method: 'POST',
      body: data,
    }).then((response) => {
      response.json().then((body) => {
        this.setState({ imageURL: `http://localhost:8000/${body.file}` });
      });
    });
  }

  render() {
    return (
      <form onSubmit={this.handleUploadImage}>
        <div>
          <input ref={(ref) => { this.uploadInput = ref; }} type="file" />
        </div>
        <div>
          <input ref={(ref) => { this.fileName = ref; }} type="text" placeholder="Enter the desired name of file" />
        </div>
        <br />
        <div>
          <button type="submit">Upload</button>
        </div>
        <img src={this.state.imageURL} alt="img" />
      </form>
    );
  }
}

export default Main;

Answer 3

更改

<form onSubmit={this.handleUploadImage}>

至

<form onSubmit={e => this.handleUploadImage(e)}>

這將僅在您單擊時調用handleUploadImage