SOURCE

const uploadEl = document.querySelector('.upload')

uploadEl.addEventListener('dragover', (e) => {
    e.preventDefault()
    e.stopPropagation()
})

uploadEl.addEventListener('drop', (e) => {
    e.preventDefault()
    e.stopPropagation()
    const files = this.files || e.dataTransfer.files
    const reader = new FileReader()
    reader.readAsText(files[0], 'utf-8')
    reader.onload = function (evt) {
        var text = evt.target.result
        dashboard.innerText = text
    }
})

<div class="upload">
拖入文件上传
</div>

<div class="view">
1
</div>

html,body {
    margin: 0;
}

body {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

.upload {
    width: 320px;
    height: 120px;
    background: #ccc;
    border-radius: 4px;
    display: flex;
    justify-content: center;
    align-items: center;
    color: #fff;
}

.view {
    width: 320px;
    height: 120px;
    margin-top: 10px;
    box-sizing: border-box;
    border-radius: 4px;
    border: 1px solid #ccc;
    overflow-y: auto;
    padding: 10px;
}