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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
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==
equal to
x == 8
false
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x == 5
true
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x == "5"
true
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===
equal value and equal type
x === 5
true
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x === "5"
false
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!=
not equal
x != 8
true
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!==
not equal value or not equal type
x !== 5
false

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x !== "5"
true

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x !== 8
true

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>
greater than
x > 8
false
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<
less than
x < 8
true
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>=
greater than or equal to
x >= 8
false
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<=
less than or equal to
x <= 8
true
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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
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&&
and
(x < 10 && y > 1) is true
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||
or
(x == 5 || y == 5) is false
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!
not
!(x == y) is true
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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


let 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 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
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2 < "12"
true
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2 < "John"
false
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2 > "John"
false
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2 == "John"
false
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"2" < "12"
false
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"2" > "12"
true
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"2" == "12"
false
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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";
}

Try it Yourself »


The Nullish Coalescing Operator (??)
The ?? operator returns the first argument if it is not nullish
(null or undefined).
Otherwise it returns the second argument.

Example

let name = null;
let text = "missing";
let result = name ?? text;

Try it Yourself »

The nullish operator is supported in all browsers since March 2020:










Chrome 80
Edge 80
Firefox 72
Safari 13.1
Opera 67


Feb 2020
Feb 2020
Jan 2020
Mar 2020
Mar 2020





The Optional Chaining Operator (?.)
The ?. operator returns undefined if an object is
undefined or null (instead of throwing an error).

Example

// Create an object:
const car = {type:"Fiat", model:"500", color:"white"};
// Ask for car name:
document.getElementById("demo").innerHTML = car?.name;

Try it Yourself »

The optional chaining operator is supported in all browsers since March 2020:










Chrome 80
Edge 80
Firefox 72
Safari 13.1
Opera 67


Feb 2020
Feb 2020
Jan 2020
Mar 2020
Mar 2020





Test Yourself With Exercises

Exercise:
Choose the correct comparison operator to alert true, when x is greater than y.


x = 10;
y = 5;
alert(x y);



Submit Answer »
Start the Exercise »














★
+1

Reference: https://www.w3schools.com/js/js_comparisons.asp