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JavaScript Comparison and Logical Operators

Comparison and Logical operators are used for testing for true or false.

How Can it Be Used?

Comparison operators can be used in conditional statements for comparing values and taking action depending on the result:

if (age < 18) text = “Too young to buy alcohol”;

Logical Operators

Logical operators determine the logic between variables or values.

Given that x = 6 and y = 3, the table below explains the logical operators.

Operator

Description

Example

Try it

&&

and

(x < 10 && y > 1) is true

Try it »

||

or

(x == 5 || y == 5) is false

Try it »

!

not

!(x == y) is true

Try it »

Conditional (Ternary) Operator

JavaScript consists of conditional operator that are used to assign a value to a variable based on some condition.

Syntax

variablename = (condition) ? value1:value2

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Comparison</h2>

<p>Input your age and click the button:</p>

<input id=”age” value=”18″

<button onclick=”myFunction()”>Try it</button>

<p id=”demo”></p>

<script>

function myFunction() {

  let age = document.getElementById(“age”).value;

  let voteable = (age < 18) ? “Too young”:”Old enough”;

  document.getElementById(“demo”).innerHTML = voteable + ” to vote.”;

}

</script>

</body>

</html>

Output

JavaScript Comparison

Input your age and click the button:

Comparing Different Types

Comparing data of different types may give unexpected results.

When a string is compared with a number, JavaScript converts the string to a number while doing the comparison. An empty string converts to 0.

CaseValue
2 < 12true
2 < “12”true
2 < “John”false
2 > “John”false
2 == “John”false
“2” < “12”false
“2” > “12”true
“2” == “12”false 

When comparing two strings, “2” will be greater than “12”, because (alphabetically) 1 is less than 2.

Variables must be converted to the proper type before comparison:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Comparisons</h2>

<p>Input your age and click the button:</p>

<input id=”age” value=”18″ />

<button onclick=”myFunction()”>Try it</button>

<p id=”demo”></p>

<script>

function myFunction() {

  let voteable;

  let age = Number(document.getElementById(“age”).value);

  if (isNaN(age)) {

    voteable = “Input is not a number”;

  } else {

    voteable = (age < 18) ? “Too young” : “Old enough”;

  }

 document.getElementById(“demo”).innerHTML = voteable + ” to vote”;

}

</script>

</body>

</html>

Output

JavaScript Comparisons

Input your age and click the button:


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