注释用于防止执行语句。编译器执行代码时, 注释将被忽略。注释是用户友好的, 因为用户可以使用注释获得代码的解释。
语法如下：
// For single line comment/* For block of lines comment
...
...
*/返回值：在执行代码期间, 注释将被忽略。
范例1：此示例说明了使用//的单行注释。
<!DOCTYPE html>
< html >
< head >
< title >
JavaScript Comments
</ title >
< script >
// Function to add two numbers
function add() {
// Declare three variables
var x, y, z;
// Input a number and store it into variable x
x = Number( document.getElementById("num1").value );
// Input a number and store it into variable x
y = Number( document.getElementById("num2").value );
// Sum of two numbers
z= x +y;
// Return the sum
document.getElementById("sum").value = z;
}
</ script >
</ head >
< body >
Enter the First number: < input id = "num1" >< br >< br >
Enter the Second number: < input id = "num2" >< br >< br >
< button onclick = "add()" >
Sum
</ button >
< input id = "sum" >
</ body >
</ html >输出如下：
在单击按钮之前：
单击按钮后：
范例2：此示例说明了使用/ *…* /的多行注释
<!DOCTYPE html>
< html >
< head >
< title >
JavaScript Comments
</ title >
< script >
/* Script to get two input from user
and add them */
function add() {
/* Declare three variable */
var x, y, z;
/* Input the two nos. num1, num2
Input num1 and store it in x
Input num2 and store it in y
The sum is stored in a variable z*/
x = Number(document.getElementById("num1").value);
y = Number(document.getElementById("num2").value);
z = x + y;
document.getElementById("sum").value = z;
}
</ script >
</ head >
< body >
Enter the First number : < input id = "num1" >< br >< br >
Enter the Second number: < input id = "num2" >< br >< br >
< button onclick = "add()" >
Sum
</ button >
< input id = "sum" >
</ body >
</ html >输出如下：
在单击按钮之前：
单击按钮后：
范例3：此示例说明注释的代码将永远不会执行。
<!DOCTYPE html>
< html >
< head >
< title >
JavaScript Comments
</ title >
< script >
function add() {
var x, y, z;
x = Number( document.getElementById("num1").value );
y = Number( document.getElementById("num2").value );
z= x +y;
// Comment the code section
//document.getElementById("sum").value = z;
}
</ script >
</ head >
< body >
Enter the First number: < input id = "num1" >< br >< br >
Enter the Second number: < input id = "num2" >< br >< br >
< button onclick = "add()" >
Sum
</ button >
< input id = "sum" >
</ body >
</ html >输出如下：
在单击按钮之前：
单击按钮后：
