Difference between != and !==
=
is an assignment operator, e.g. If you run var x = 1;
then x
will have the value of 1
.
==
(or !=
) is a comparison operator that checks if the value of something is equal to the value of something else. e.g. if(x == 1)
will evaluate to true
and so will if(x == true)
because 1
will evaluate to true
and 0
evaluate to false
.
===
(or !==
) is another comparison operator that checks if the value of something is equal to the value of, and is the same type as something else. e.g. if(x === 1)
will evaluate to true
however, if(x === true)
will evaluate to false
because 1
(the value of x
) is an integer and true
is a boolean.
Difference between == and === in JavaScript
===
and !==
are strict comparison operators:
JavaScript has both strict and
type-converting equality comparison.
Forstrict
equality the objects being
compared must have the same type and:
- Two strings are strictly equal when they have the same sequence of
characters, same length, and same
characters in corresponding positions.- Two numbers are strictly equal when they are numerically equal (have
the same number value).NaN
is not
equal to anything, includingNaN
.
Positive and negative zeros are equal
to one another.- Two Boolean operands are strictly equal if both are true or
both are false.- Two objects are strictly equal if they refer to the same
Object
.Null
andUndefined
types are==
(but not===
). [I.e. (Null==Undefined
) istrue
but (Null===Undefined
) isfalse
]
Comparison Operators - MDC
Difference between == and ===
In short:
==
operator checks if their instance values are equal, "equal to"
===
operator checks if the references point the same instance, "identical to"
Long Answer:
Classes are reference types, it is possible for multiple constants and variables to refer to the same single instance of a class behind the scenes. Class references stay in Run Time Stack (RTS) and their instances stay in Heap area of Memory. When you control equality with ==
it means if their instances are equal to each other. It doesn't need to be same instance to be equal. For this you need to provide a equality criteria to your custom class. By default, custom classes and structures do not receive a default implementation of the equivalence operators, known as the “equal to” operator ==
and “not equal to” operator !=
. To do this your custom class needs to conform Equatable
protocol and it's static func == (lhs:, rhs:) -> Bool
function
Let's look at example:
class Person : Equatable {
let ssn: Int
let name: String
init(ssn: Int, name: String) {
self.ssn = ssn
self.name = name
}
static func == (lhs: Person, rhs: Person) -> Bool {
return lhs.ssn == rhs.ssn
}
}
P.S.:
Since ssn(social security number) is a unique number, you don't need to compare if their name are equal or not.
let person1 = Person(ssn: 5, name: "Bob")
let person2 = Person(ssn: 5, name: "Bob")
if person1 == person2 {
print("the two instances are equal!")
}
Although person1 and person2 references point two different instances in Heap area, their instances are equal because their ssn numbers are equal. So the output will be the two instance are equal!
if person1 === person2 {
//It does not enter here
} else {
print("the two instances are not identical!")
}
===
operator checks if the references point the same instance, "identical to"
. Since person1 and person2 have two different instance in Heap area, they are not identical and the output the two instance are not identical!
let person3 = person1
P.S:
Classes are reference types and person1's reference is copied to person3 with this assignment operation, thus both references point the same instance in Heap area.
if person3 === person1 {
print("the two instances are identical!")
}
They are identical and the output will be the two instances are identical!
What is difference between == and === in kotlin
In Kotlin, two types of equality are available. These are: Structural Equality & Referential Equality.
class A {
var foo = 1
}
var a1 = A()
var a2 = A()
Here a1
and a2
are two instances of class A
.
println(a1 == a2)
It prints false
because a1
and a2
are not structurally equal.
println(a1 === a2)
It prints false
because a1
and a2
are not referencing the same object.
But, if you execute this line: a1 = a2
then,
a1 and a2 will be structurally equal and a1 is referencing to the a2 instance. That's why,
println(a1 == a2)
println(a1 === a2)
both these lines returns true.
What is the difference between the `=` and `==` operators and what is `===`? (Single, double, and triple equals)
=
is the assignment operator. It sets a variable (the left-hand side) to a value (the right-hand side). The result is the value on the right-hand side.
==
is the comparison operator. It will only return true
if both values are equivalent after coercing their types to the same type.
===
is a more strict comparison operator often called the identity operator. It will only return true
if both the type and value of the operands are the same.
I would check out CodeCademy for a quick intro to JavaScript.
If you prefer to read more, MDN is a great intro as well.
For those concerned about the source of the term "identity operator" jbabey pointed out that JavaScript: The Definitive Guide seems to mention it.
Difference between == and === in JS
There are lots of answers to this question on Stackoverflow already.
Short:
==
only compares values
===
compares values + type
var check1 = '10',
check2 = 10;
check1 == check2 // true
check1 === check2 // false
Which equals operator (== vs ===) should be used in JavaScript comparisons?
The strict equality operator (===
) behaves identically to the abstract equality operator (==
) except no type conversion is done, and the types must be the same to be considered equal.
Reference: Javascript Tutorial: Comparison Operators
The ==
operator will compare for equality after doing any necessary type conversions. The ===
operator will not do the conversion, so if two values are not the same type ===
will simply return false
. Both are equally quick.
To quote Douglas Crockford's excellent JavaScript: The Good Parts,
JavaScript has two sets of equality operators:
===
and!==
, and their evil twins==
and!=
. The good ones work the way you would expect. If the two operands are of the same type and have the same value, then===
producestrue
and!==
producesfalse
. The evil twins do the right thing when the operands are of the same type, but if they are of different types, they attempt to coerce the values. the rules by which they do that are complicated and unmemorable. These are some of the interesting cases:'' == '0' // false
0 == '' // true
0 == '0' // true
false == 'false' // false
false == '0' // true
false == undefined // false
false == null // false
null == undefined // true
' \t\r\n ' == 0 // true
The lack of transitivity is alarming. My advice is to never use the evil twins. Instead, always use
===
and!==
. All of the comparisons just shown producefalse
with the===
operator.
Update:
A good point was brought up by @Casebash in the comments and in @Phillipe Laybaert's answer concerning objects. For objects, ==
and ===
act consistently with one another (except in a special case).
var a = [1,2,3];
var b = [1,2,3];
var c = { x: 1, y: 2 };
var d = { x: 1, y: 2 };
var e = "text";
var f = "te" + "xt";
a == b // false
a === b // false
c == d // false
c === d // false
e == f // true
e === f // true
The special case is when you compare a primitive with an object that evaluates to the same primitive, due to its toString
or valueOf
method. For example, consider the comparison of a string primitive with a string object created using the String
constructor.
"abc" == new String("abc") // true
"abc" === new String("abc") // false
Here the ==
operator is checking the values of the two objects and returning true
, but the ===
is seeing that they're not the same type and returning false
. Which one is correct? That really depends on what you're trying to compare. My advice is to bypass the question entirely and just don't use the String
constructor to create string objects from string literals.
Reference
http://www.ecma-international.org/ecma-262/5.1/#sec-11.9.3
Difference between == and === in Scala, Spark
The "==
" is using the equals
methods which checks if the two references point to the same object. The definition of "===
" depends on the context/object. For Spark , "===
" is using the equalTo
method.
See
- for
==
https://spark.apache.org/docs/2.0.0/api/java/org/apache/spark/sql/Column.html#equals(java.lang.Object) - for
===
https://spark.apache.org/docs/2.0.0/api/java/org/apache/spark/sql/Column.html#equalTo(java.lang.Object)
(Since you are referencing Spark:) An important difference for Spark is the return value. For Column:
==
returns a boolean===
returns a column (which contains the result of the comparisons of the elements of two columns)
Related Topics
Any Way to Replace Characters on Swift String
How to Resolve "Ambiguous Use Of" Compile Error With Swift #Selector Syntax
Formatting Input For Currency With Nsnumberformatter in Swift
How to Set Layer Cornerradius For Only Bottom-Left, Bottom-Right, and Top-Left Corner
Call a Method from a String in Swift
Unwrapping Multiple Optionals in If Statement
Providing a Default Value For an Optional in Swift
Deletable Table With Textfield on Swiftui
How to Remove the Left and Right Padding of a List in Swiftui
Knowing Where Retain Cycles Are and Removing Them
Shall We Always Use [Unowned Self] Inside Closure in Swift
How to Convert a Date String With Optional Fractional Seconds Using Codable in Swift
Sort Dictionary by Values in Swift
Real Time Nstask Output to Nstextview With Swift
How to Generate a Random Number in a Range (10...20) Using Swift
Custom Back Button For Navigationview'S Navigation Bar in Swiftui