JavaScript 注释可用于解释 JavaScript 代码,以及 使其更具可读性。
JavaScript 注释也可以用来阻止执行,当 测试替代代码。
单行注释以 //
开头。
JavaScript 将忽略 //
和行尾之间的任何文本 (不会被执行)。
此示例在每个代码行之前使用单行注释:
// Change heading:
document.getElementById("myH").innerHTML = "My First Page";
// Change paragraph:
document.getElementById("myP").innerHTML = "My first paragraph.";
自己尝试一下→
<!DOCTYPE html>
<html>
<body>
<h1 id="myH"></h1>
<p id="myP"></p>
<script>
// Change heading:
document.getElementById("myH").innerHTML = "JavaScript Comments";
// Change paragraph:
document.getElementById("myP").innerHTML = "My first paragraph.";
</script>
</body>
</html>
此示例在每行末尾使用单行注释 解释一下代码:
let x = 5; // Declare x, give it the value of 5
let y = x + 2; // Declare y, give it the value of x + 2
自己尝试一下 →
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Comments</h2>
<p id="demo"></p>
<script>
let x = 5; // Declare x, give it the value of 5
let y = x + 2; // Declare y, give it the value of x + 2
// Write y to demo:
document.getElementById("demo").innerHTML = y;
</script>
</body>
</html>
多行注释以 /*
开头,以 */
结尾。
JavaScript 将忽略 /*
和 */
之间的任何文本。
本例使用多行注释(注释块)来解释代码:
/*
The code below will change
the heading with id = "myH"
and the paragraph with id = "myP"
in my web page:
*/
document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";
自己尝试一下→
<!DOCTYPE html>
<html>
<body>
<h1 id="myH"></h1>
<p id="myP"></p>
<script>
/*
The code below will change
the heading with id = "myH"
and the paragraph with id = "myP"
*/
document.getElementById("myH").innerHTML = "JavaScript Comments";
document.getElementById("myP").innerHTML = "My first paragraph.";
</script>
</body>
</html>
最常见的是使用单行注释。
块注释通常是 用于正式文档。
使用注释来阻止代码执行适用于 代码测试。
在代码行前面添加 //
将代码行从可执行行更改为 一条评论。
此示例使用/来阻止执行以下代码行之一:
//document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";
自己尝试一下 →
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Comments</h2>
<h1 id="myH"></h1>
<p id="myP"></p>
<script>
//document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";
</script>
<p>The line starting with // is not executed.</p>
</body>
</html>
此示例使用注释块来阻止执行 多行:
/*
document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";
*/
自己尝试一下 →
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Comments</h2>
<h1 id="myH"></h1>
<p id="myP"></p>
<script>
/*
document.getElementById("myH").innerHTML = "Welcome to my Homepage";
document.getElementById("myP").innerHTML = "This is my first paragraph.";
*/
document.getElementById("myP").innerHTML = "The comment-block is not executed.";
</script>
</body>
</html>