模仿一个在线表格

* {
    box-sizing: border-box;
}

body {
    margin: 0;
}

.tools {
    width: 100%;
    height: 30px;
    background-color: #efefef;
    margin-bottom: 20px;
}

table {
    width: 2889px;
    table-layout: fixed;
    border-collapse: collapse;
    font-size: 12px;
}

table,
th,
td {
    border: 0.5px solid #d9d9dd;
}

table th,
table td {
    width: 107px;
    height: 22px;
    font-weight: 300;
    padding: 0;
    margin: 0;
}

table th {
    font-weight: 400;
    background-color: #efefef;
}

table td textarea {
    display: block;
    width: 107px;
    height: 22px;
    line-height: 22px;
    border: none;
    padding: 0 5px;
    margin: 0;
    resize: none;
    cursor: default;
}

table td textarea:focus {
    outline: none;
    border: 2px solid lightskyblue;
    line-height: 18px;
}

var table = document.getElementsByTagName('table')[0]
// 1. 完成表格中的行标题
var headTrElement = document.createElement('tr')
var headInfo = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z']
for (var i = 0; i < 27; i++) {
    var HeadThElement = document.createElement('th')
    //从第2个开始显示标题
    if (i > 0) {
        HeadThElement.textContent = headInfo[i - 1]
    }
    headTrElement.appendChild(HeadThElement)
}
table.appendChild(headTrElement)
// 2. 完成表格
for (var i = 0; i < 200; i++) {
    var trElement = document.createElement("tr")
    // 完成表格内容
    var thElement = document.createElement("th")
    thElement.textContent = i + 1
    trElement.appendChild(thElement)
    for (var j = 0; j < 26; j++) {
        var TdThElement = document.createElement('td')

        trElement.appendChild(TdThElement)
    }
    table.appendChild(trElement)
}

for (var j = 0; j < 26; j++) {
    var tdElement = document.createElement('td')
    // 加入文本
    var textareaElement = document.createElement('textarea')
    textareaElement.setAttribute('rows', '1')
    textareaElement.setAttribute('readonly', 'readonly')
    tdElement.appendChild(textareaElement)

    trElement.appendChild(tdElement)
}

var target = event.target
var trElement = tdElement.parentNode
var thElement = trElement.firstChild
thElement.style.backgroundColor = '#d9d9dd'

// 当前的<td>元素是<tr>元素的第几个子元素
var tdElements = trElement.childNodes
// 将tdElements转化为数组
var arr = Array.prototype.slice.call(tdElements)
// 获取当前点击的单元格所在列的索引
var index = arr.indexOf(tdElement)
console.log(index)
var headTrElement = table.getElementsByTagName('tr')[0]
var headThElements = headTrElement.getElementsByTagName('th')
var targetThElement = headThElements.item(index)
targetThElement.style.backgroundColor = '#d9d9dd'

focusTdElement.ondblclick = function () {
    var target = event.target
    var textareaElement
    if (target.nodeName === 'TEXTAREA') {
        textareaElement = target
    } else if (target.nodeName === 'TD') {
        textareaElement = target.firstChild
    }
    textareaElement.removeAttribute('readonly')
}