本文主要实现，h5通过input上传图片后，利用cropperjs进行裁剪，获取指定尺寸

1 安装cropperjs

npm install cropperjs 

2 具体实现

home.jsx
代码中的result模块用来展示最终的裁剪结果；mask用作页面最上层蒙层，用来裁剪上传的图片

import React, { memo, useEffect, useState, useRef } from 'react'
import 'cropperjs/dist/cropper.css'
import Cropper from 'cropperjs'
import cn from './home.module.scss'

let myCropper = null // 创建cropper全局对象

function Home() {
    const [uploadImg, setUploadImg] = useState('') // 上传图像的地址
    const [cropperImg, setCropperImg] = useState('') // 裁剪后的图像地址
    const imgRef = useRef()

    const initCrop = () => { // 初始化
        myCropper = new Cropper(imgRef.current, {
            viewMode: 1, // 视图控制
            dragMode: 'none', // 拖拽图片模式
            aspectRatio: 1, // 裁剪框为固定的宽高比
            autoCropArea: 0.6, // 设置裁剪区域占图片的大小 值为 0-1 默认 0.8 表示 80%的区域
            zoomOnWheel: false, // 是否可以通过鼠标滚轮缩放图片 默认true
        })
    }

    const cancel = () => { // 销毁
        myCropper.destroy() // 销毁cropper
        myCropper = null
    }

    const handleCrop = async () => { // 裁剪
        setUploadImg('')
        myCropper.getCroppedCanvas({
            imageSmoothingQuality: 'high'
        }).toBlob(async (blob) => {
        // 设置个文件名，不然文件名就是默认的“blob”
        const file = new File([blob], 'result.png')
        const img = window.URL.createObjectURL(file)
        setCropperImg(img)
        cancel()
        })
    }

    const handleUpload = async (e) => { // 上传
        const file = e.target.files[0]
        const img = window.URL.createObjectURL(file) // 上传图片的blob地址
        setUploadImg(img)
        setTimeout(() => {
            initCrop() // 开始裁剪
        }, 0)
    }

    return <div className={cn.main}>
        <input
            className={cn.item_input}
            type={'file'}
            accept={'image/*'}
            onChange={handleUpload}
        />
        <div className={cn.result}>
            {
                cropperImg && <img src={cropperImg} alt='' className={cn.result_cropper} />
            }
        </div>
        {
            uploadImg && <div className={cn.mask}>
                <div className={cn.mask_btn} onClick={handleCrop}>裁剪</div>
                <img ref={imgRef} className={cn.mask_cropper} src={uploadImg} alt='' />
            </div>
        }
    </div>
}

home.module.scss

.input {
  margin: auto;
  height: 50px;
}

.result {
  position: relative;
  margin: auto;
  height: 300px;
  width: 100%;

  &_cropper {
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
    max-width: 100%;
    max-height: 100%;
    object-fit: contain;
  }
}

.mask {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  background: rgba(0, 0, 0, 0.7);

  &_btn {
    position: absolute;
    z-index: 10;
    right: 0;
    top: 0;
    width: 100px;
    height: 100px;
    font-size: 28px;
    font-weight: 450;
    line-height: 100px;
    color: #FFFFFF;
  }

  &_cropper {
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
    max-width: 100%;
    max-height: 100%;
    object-fit: contain;
  }
}