JavaScript Comparison and Logical Operators


Comparison and Logical operators are used to test for true or false.


Comparison Operators

Comparison operators are used in logical statements to determine equality or difference between variables or values.

Given that x = 5, the table below explains the comparison operators:

Operator Description Comparing Returns Try it
== equal to x == 8 false Try it »
x == 5 true Try it »
=== equal value and equal type x === "5" false Try it »
x === 5 true Try it »
!= not equal x != 8 true Try it »
!== not equal value or not equal type x !== "5" true Try it »
x !== 5 false Try it »
> greater than x > 8 false Try it »
< less than x < 8 true Try it »
>= greater than or equal to x >= 8 false Try it »
<= less than or equal to x <= 8 true Try it »

How Can it be Used

Comparison operators can be used in conditional statements to compare values and take action depending on the result:

if (age < 18) text = "Too young";

You will learn more about the use of conditional statements in the next chapter of this tutorial.


Logical Operators

Logical operators are used to 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 also contains a conditional operator that assigns a value to a variable based on some condition.

Syntax

variablename = (condition) ? value1:value2 

Example

var voteable = (age < 18) ? "Too young":"Old enough";

Try it Yourself »

If the variable age is a value below 18, the value of the variable voteable will be "Too young", otherwise the value of voteable will be "Old enough".


Comparing Different Types

Comparing data of different types may give unexpected results.

When comparing a string with a numeric constant, JavaScript will treat the number as a string when doing the comparison. The result of this is commonly not the same as a numeric comparison.

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

To secure a proper result, variables should be converted to the proper type before comparison:

age = Number(age);
if (isNaN(age)) {
    voteable = "Error in input";
} else {
    voteable = (age < 18) ? "Too young" : "Old enough";
}

Try it Yourself »
Note The Number() function converts an empty string to 0, and a non numeric string to NaN.

JavaScript Bitwise Operators

Bit operators work on 32-bit numbers.

Any numeric operand in the operation is converted into a 32-bit number.

The result is converted back to a JavaScript number.

Example

x = 5 & 1;

The result in x:

1

Try it Yourself »

Operator Description Example Same as Result Decimal
& AND x = 5 & 1 0101 & 0001 0001 1
| OR x = 5 | 1 0101 | 0001 0101 5
~ NOT x = ~ 5  ~0101 1010 10
^ XOR x = 5 ^ 1 0101 ^ 0001 0100 4
<< Left shift x = 5 << 1 0101 << 1 1010 10
>> Right shift x = 5 >> 1 0101 >> 1 0010 2

Note The examples above uses 4 bits unsigned examples. But JavaScript uses 32-bit signed numbers.

Because of this, in JavaScript, ~ 5 will not return 10. It will return -6.

~00000000000000000000000000000101 will return 11111111111111111111111111111010


Test Yourself with Exercises!

Exercise 1 »  Exercise 2 »  Exercise 3 »  Exercise 4 »  Exercise 5 »  Exercise 6 »



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