innerText
innerText 属性只返回文本，不包含段落外空格和内部元素标签。
<body>
<p id="para"> This is a <span>test</span> paragraph. </p>
</body>
<script>
consoel.log(document.getElementById('para').innerText);
// "This is a test paragraph."
</script>
innerHTML
innerHTML 属性返回文本，包含所有空格和内部元素标签。
<body>
<p id="para"> This is a <span>test</span> paragraph. </p>
</body>
<script>
consoel.log(document.getElementById('para').innerText);
// " This is a <span>test</span> paragraph. "
</script>
textContent
textContent 属性返回带空格的文本，但是不包含内部元素标签。
<body>
<p id="para"> This is a <span>test</span> paragraph. </p>
</body>
<script>
consoel.log(document.getElementById('para').innerText);
// " This is a test paragraph. "
</script>
