This question already has answers here:
Which equals operator (== vs ===) should be used in JavaScript comparisons?
(48 answers)
Closed 9 years ago.
I found == is little confusing for newbies, So I want someone to explain how it works.
For example -
new String("a") == "a" and "a" == new String("a") are both true.
new String("a") == new String("a") is false.
Why?
== is called comparison/equality operator, it compares 2 values, but not their data types so for example
1 == '1' will return true, for stricter comparison, use === which will compare the data types too so 1 === '1' will return false
== is a comparison operator that means "equal to" but does not take variable typing into account.
=== is a stricter comparison operator that means "equal to and same type".
So if you have a string called numberStr with a value of 2 and an integer called numberInt with a value of 2, they will evaluate as follows:
numberStr == numberInt // evaluates to true
numberStr === numberInt // evaluates to false because types are different
Related
This question already has answers here:
Why `null >= 0 && null <= 0` but not `null == 0`?
(6 answers)
Closed 2 years ago.
How should I understand these?
null>0
> false
null==0
> false
null>=0
> true
The relational operators (>= and <=), perform type coercion (ToPrimitive), with a hint type of Number, all the relational operators present have this behavior.
You can see the inner details of this process in the The Abstract Relational Comparison Algorithm.
On the other hand, the Equals operator (==), if an operand is null it only returns true if the other is either null or undefined, no numeric type coercion is made.
null == undefined; // true
null == null; // true
Check the inner details of this process in the The Abstract Relational Comparison Algorithm.
Recommended articles:
typeof, == and ===
Notes on ECMAScript Equality Operators
The relative comparison operators imply a numeric context, so in those cases (>, >=) the null is converted to a number (zero).
In the == case, however, both values are treated as boolean values, and Javascript doesn't think that null should be equal to any other "falsy" values. It's kind-of weird. The equality algorithm for == has a bunch of special cases, and null is one of those. It's only == to itself and undefined.
When null is used in a numeric experession it evalutes to 0, that explains your > and >= cases.
== is more subtle. Informally, null is not the same as zero, so it kind of makes sense.
Interesting! It seems like Javascript needs a couple new identity operators like >== and <==. Although I am not sure that would make much sense, given the numerical implications of > and <.
This gives the expected result...
(null > 0 || null === 0);
in dreamweaver cc 2015, when i am using the comparison operators in jquery/javascript programming like:
if(x == "")
DW shows an error that Expected === and instead saw ==. My question is that what is the difference between === and == ?.
As i know in other languages like C# etc the === operator means that the comparison will check the Data Type of the value as well as the value. In javascript or jquery is there any problem if i use the == instead of === ? or still the result will be the same in jquery / javascript?
In Javascript, === do not try to coerce the type of the variables you are testing, while == will do its best to 'typecast' those variables if needed to compare them.
For instance 1 == '1' returns true, while 1 === '1' returns false since you are comparing a number to a string.
Lastly, jQuery and pure javascript both uses the same === and == operators. Hence, there will not be any difference between the two.
The MDN documentation is pretty good too.
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.
For more you can check this answer in stack oveflow
Which equals operator (== vs ===) should be used in JavaScript comparisons?
There is a slight difference between == and === operators. If you are using == that means you are comparing just values for example (5=='5') will return you true whereas first operand is integer and the second operand is string.Now considering the same example with === i.e (5==='5') will return you false because the '===' operator will check the value as well as type conversion and in this case integer cannot be equal to the string. Hope this helps you.
This question already has answers here:
Which equals operator (== vs ===) should be used in JavaScript comparisons?
(48 answers)
Closed 7 years ago.
I am trying to understand equality in JavaScript. Here is the code.
var x = prompt("What is 10 + 10");
if (x === 10) {
document.write("Correct")
}
else {
document.write("Incorrect")
}
Why wouldn't I make the equals sign like "===". So if "10" is equal("===") to "x"(user answer) then it should be correct right?
I searched on both Stack Overflow and W3Schools, but couldn't find what I was looking for. I guess I'm just nor getting this "true or false" thing. I mean this seems like a very simple equation. Help would be great thanks guys!
=== is strict type equality which compares by both value and type
== is non-strict type equality, which compares only by value.
In other words, == performs type conversion and then compares values for equality. Here are some examples
"3" == 3
=> true
Explanation: The string 3 is converted to the number 3, which is equal to 3.
"3" === 3
=> false
Explanation: The string is not converted to a number. Thus the string 3 does not equal the number 3.
In your example, incorrect would be written to the document. That is because the result of prompt returns a string, and you are performing strict equality with a number.
In your case, the interpreter sees it like this
if ("10" === 10) {
// does the string "10" equal the number 10? If so
document.write("Correct")
}
else {
// Hey, wait a minute. It doesn't equal the number. I should write "Incorrect" instead.
document.write("Incorrect")
}
In Javascript,
== means: is equivalent to
=== means: is identical to
When the value of x is "10", x is equivalent to 10.
But it isn't identical to 10.
This question already has answers here:
Which equals operator (== vs ===) should be used in JavaScript comparisons?
(48 answers)
Closed 8 years ago.
[4] === 4 // is: false
[4] == 4 // is: true
'0' == 0 // is: true
'0' === 0 // is: false
Can anyone give the exact reason for this?Also what exactly does strict equality operator do or need for comparision?I learned that type and value should be same for strict(===) operator.Is this what strict equality operator checks .If yes,than how equl to operator works?
== Compare values
=== Compare values and type
For example
[4] //turns into "4" when comparing
"4" == 4 //They are the same
"4" === 4 //The values are the same, but not the type
Reference: http://es5.github.io/#x11.9.4
http://i.stack.imgur.com/q13LO.png
The === operator also compares the type of the object.
So, in [4] === 4
[4] is an array, but 4 is a number, so that evaluates to false.
And in '0' === 0
'0' is a string, but 0 is a number, so that evaluates to false.
The === operator compares both type and value, making it a stricter check.
The == operator performs a less strict value based checked. It will in some cases consider values of different types "equal" Such examples are 0 vs '' or 0 vs "0"
The == operator will see 0 and '' as equal whereas the === operator will not treat them as equal since they are of different types.
This question already has answers here:
Closed 13 years ago.
Possible Duplicate:
Javascript === vs ==
What's the diff between "===" and "==" ? Thanks!
'===' means equality without type coersion. In other words, if using the triple equals, the values must be equal in type as well.
e.g.
0==false // true
0===false // false, because they are of a different type
1=="1" // true, auto type coersion
1==="1" // false, because they are of a different type
Source: http://longgoldenears.blogspot.com/2007/09/triple-equals-in-javascript.html
Ripped from my blog: keithdonegan.com
The Equality Operator (==)
The equality operator (==) checks whether two operands are the same and returns true if they are the same and false if they are different.
The Identity Operator (===)
The identity operator checks whether two operands are “identical”.
These rules determine whether two values are identical:
They have to have the same type.
If number values have the same value they are identical, unless one or both are NaN.
If string values have the same value they are identical, unless the strings differ in length or content.
If both values refer to the same object, array or function they are identical.
If both values are null or undefined they are identical.
The === operator means "is exactly equal to," matching by both value and data type.
The == operator means "is equal to," matching by value only.
It tests exact equality of both value and type.
given the assignment
x = 7
x===7 is true
x==="7" is false
In a nutshell "===" tests for the equality of value AND of type:
From here: