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 »
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";
»
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";
}
»
0 comments: