JavaScript Comparison and Logical Operators

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JavaScript Comparison  and Logical Operators
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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 »
x == "5" true Try it »
=== equal value and equal type x === 5 true Try it »
x === "5" false Try it »
!= not equal x != 8 true Try it »
!== not equal value or not equal type x !== 5 false Try it »
x !== "5" true Try it »
x !== 8 true 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";
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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 number, JavaScript will convert the string to a number when doing the comparison. An empty string converts to 0. A non-numeric string converts to NaN which is always false.

Case Value Try
2 < 12 true Try it »
2 < "12" true Try it »
2 < "John" false Try it »
2 > "John" false Try it »
2 == "John" false Try it »
"2" < "12" false Try it »
"2" > "12" true Try it »
"2" == "12" false Try it »
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";
}
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Test Yourself with Exercises!
Exercise 1 »  Exercise 2 »  Exercise 3 »  Exercise 4 »  Exercise 5 »  Exercise 6 »


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