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Javascript Comparisons

2 min read

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  
== equal to x == 8 false  
x == 5 true  
x == “5” true  
=== equal value and equal type x === 5 true  
x === “5” false  
!= not equal x != 8 true  
!== not equal value or not equal type x !== 5 false  
x !== “5” true  
x !== 8 true  
> greater than x > 8 false  
< less than x < 8 true  
>= greater than or equal to x >= 8 false  
<= less than or equal to x <= 8 true  

 

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 to buy alcohol";

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  
&& and (x < 10 && y > 1) is true  
|| or (x == 5 || y == 5) is false  
! not !(x == y) is true  

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";

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  
2 < 12 true  
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.

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

 
age = Number(age); if (isNaN(age)) { voteable = "Input is not a number"; } else { voteable = (age < 18) ? "Too young" : "Old enough"; }

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