Comparison and logical operators are used to test true or false.
Comparison operators
Comparison operators are used in logical statements to determine Whether variables or values are equal.
Given x=5, the following table explains the comparison operators:
| Operator | Description | Example |
|---|
| == | is equal to | x==8 is false |
| === | Congruent (value and type) | x===5 is true; x==="5" is false |
| != | is not equal to | x!=8 is true |
| > | is greater than | x>8 is false |
| < | is less than | x<8 is true |
##>= | is greater than or equal to | x>=8 is false |
<= | is less than or equal to | x<=8 is true |
How to use
You can use comparison operators in conditional statements to compare values and then take action based on the results:
if (age<18) document.write("Too young");
We will introduce more about it in the following chapters Knowledge of conditional statements.
Logical Operators
Logical operators are used to determine the logic between variables or values.
Given x=6 and y=3, the following table explains the logical operators:
Operator | Description | Example |
&& | and | (x < 10 && y > 1) is true |
|| | or | (x==5 || y==5) is false |
! | not | !(x==y) is true |
Conditional operators
JavaScript also includes conditional operators that assign values to variables based on certain conditions.
Syntax
variablename=(condition)?value1:value2
Example
If the value in the variable age is less than 18, assign the value "age is too young" to the variable voteable, otherwise assign the value "age has reached".
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>php中文网(php.cn)</title>
</head>
<body>
<p>点击按钮检测年龄。</p>
年龄:<input id="age" value="18" />
<p>是否达到投票年龄?</p>
<button onclick="myFunction()">点击按钮</button>
<p id="demo"></p>
<script>
function myFunction()
{
var age,voteable;
age=document.getElementById("age").value;
voteable=(age<18)?"年龄太小":"年龄已达到";
document.getElementById("demo").innerHTML=voteable;
}
</script>
</body>
</html>Run the program and try it
Next Section<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>php中文网(php.cn)</title>
</head>
<body>
<p>点击按钮检测年龄。</p>
年龄:<input id="age" value="18" />
<p>是否达到投票年龄?</p>
<button onclick="myFunction()">点击按钮</button>
<p id="demo"></p>
<script>
function myFunction()
{
var age,voteable;
age=document.getElementById("age").value;
voteable=(age<18)?"年龄太小":"年龄已达到";
document.getElementById("demo").innerHTML=voteable;
}
</script>
</body>
</html>
