Javascript Is Equal To

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There are four ways to compare equality in JavaScript. This article discusses the unique operators used to determine equality, what kind of coercion is, and some of the peculiarities encountered when evaluating a true or false value in JavaScript.

Strict equality is represented by a triple equal sign (===). The purpose of this operator is to compare not only the value, but also its type.

strictComparison in the example above accepts two values ‚Äã‚Äãand returns if the two values ‚Äã‚Äãare strictly equal to each other.

At first glance, the values ‚Äã‚Äãlook the same because they are both 8. However, the strict equality operator also examines the type. If we were to look at a in this case, and look at typeof a returns ’number’. If we were to do the same with b, with typeof b it would return ’string’.

Since the types are not the same, it returns false.

unusual comparisons with ===

There are some unusual comparisons that can be made with the strict equality operator in JavaScript. Here are some of those that are commonly requested in interview situations:

Operand1 typeof Operand1 Operand2 typeof Operand2 return value
null object null object true
undefined undefined undefined undefined true
null object undefined undefined false
NaN number NaN number false
false boolean "false" string false
false boolean false boolean true
"" string "" string true
"& rdquo string undefined undefined false

Another thing to note is that this does not not going to compare with data structures. You need to use a more sophisticated instruction to compare arrays or objects.

Most of the entries here evaluate well because the types match or don’t match. The only exception is NaN - this returns false due to the fact that NaN can theoretically be anything - so there is no indication as to whether it might be the same or not, hence the assessment as false.

Strict inequality comparison

The strict inequality operator is represented by an exclamation point and two equal signs (! ==). two values ‚Äã‚Äãare not equal the value and the type.

The strictInequalityComparison function in the example above accepts two values ‚Äã‚Äãand returns if the two values ‚Äã‚Äãare not strictly equal to each other.

At first glance, the values ‚Äã‚Äãseem equal (not unequal) because both have the same value.However, the strict inequality operator, like the strict equality operator, also gua rda type.

If we were to look at a in this case, and look at typeof a, will return ’string’. If we were to do the same with b, with typeof b it would return ’Number’ . Since the types are not the same, it will return true.

unusual comparisons with! ==

There are some unusual comparisons that can be made with the strict inequality operator in JavaScript. Here are some of the frequently asked questions in interview situations:

Operand1 typeof Operand1 Operand2 typeof Operand2 return value
null object null object false
undefined undefined undefined undefined false
null object undefined undefined true
NaN number NaN number true
false < / td> boolean "false" string true
false boolean false boolean false
"" string "" string false
"" string undefined undefined true

Just like with the strict equality operator , no comparison between objects or arrays is possible.

One thing ...

In most situations in your JavaScript development career, these two operators, the = == and the! = =, will be the ones you write your conditional logic with.

The free equality operator is represented by a double equal sign (==). The purpose of this operator is to force the two values ‚Äã‚Äãto a common type before evaluating whether they are equal or not. This is called type constraint or type conversion.

looseComparison in the example above accepts two values ‚Äã‚Äãand returns whether or not the two values ‚Äã‚Äãare equal to each other.

At first glance, the values ‚Äã‚Äãdon’t look the same because one is a number and one is a string. However, the free equality operator does not look at the type. The declaration will attempt to force the types to be the same before comparing the value - so the example returns true because the second operand is converted to a number and then compared.

unusual comparisons with ==

There are some unusual comparisons that can be made with the strict equality operator in JavaScript. Here are some of the most frequently asked questions in interview situations:

Operand1 typeof Operand1 Operand2 typeof Operand2 return value
null object null object true
undefined undefined undefined undefined true
null object undefined undefined true
NaN number NaN number false
false boolean "false" string false
false boolean false boolean true
"" string "" string true
"& rdquo string undefined undefined false

Most e nts Note here same as they did in the first section on strict equality. The notable exception is that null and undefined the rough comparison returns true.

Comparison of bulk inequalities

The loose inequality operator is represented by an exclamation point and an equal sign (! =). It will assess whether the two values ‚Äã‚Äãare equal not only in value. It does this by trying to convert the two arguments to be of the same type.

looseInequalityComparison In the example above takes two values ‚Äã‚Äãand returns whether or not the two values ‚Äã‚Äãare equal to each other.

At first glance, the values look the same because they both have the same same value.However, the loose inequality operator, like the loose equality operator, forces the gender to be the same on both operands before since the values ‚Äã‚Äãare the same after the constraint , it returns false.

unusual comparisons with =

There are some unusual comparisons that can be made with the loose inequality operator in JavaScript.

Operand1 type of Operand1 operand2 type of operand2 return value
null object null object false
undefined undefined undefined and undefined false
null object undefined undefined false
NaN number < / td> NaN number true
false boolean "false" string true
false boolean false boolean false
"" s string "" string false
"" string undefined undefined true

Just like with the strict equality operator makes it impossible to make comparisons between objects or arrays.

most of the articles reviewed here as in the second section on strict inequality. The notable exception is that null and undefined pretty much yield versus false

Conclusion

This article examined the four ways to compare equality in JavaScript. The main thing to remember is that triple equality (===) and double equality (==) are not the same operator. One rigorously evaluates the type and the value and the other evaluates the value only after trying to force them both to be of the same type.

👻 Read also: what is the best laptop for engineering students?

Javascript Is Equal To JavaScript: Questions

JavaScript

JSON datetime between Python and JavaScript

4 answers

kevin By kevin

I want to send a datetime.datetime object in serialized form from Python using JSON and de-serialize in JavaScript using JSON. What is the best way to do this?

403

Answer #1

You can add the "default" parameter to json.dumps to handle this:

date_handler = lambda obj: (
    obj.isoformat()
    if isinstance(obj, (datetime.datetime, datetime.date))
    else None
)
json.dumps(datetime.datetime.now(), default=date_handler)
""2010-04-20T20:08:21.634121""

Which is ISO 8601 format.

A more comprehensive default handler function:

def handler(obj):
    if hasattr(obj, "isoformat"):
        return obj.isoformat()
    elif isinstance(obj, ...):
        return ...
    else:
        raise TypeError, "Object of type %s with value of %s is not JSON serializable" % (type(obj), repr(obj))

Update: Added output of type as well as value.
Update: Also handle date

Javascript Is Equal To JavaScript: Questions

JavaScript

What blocks Ruby, Python to get Javascript V8 speed?

4 answers

Are there any Ruby / Python features that are blocking implementation of optimizations (e.g. inline caching) V8 engine has?

Python is co-developed by Google guys so it shouldn"t be blocked by software patents.

Or this is rather matter of resources put into the V8 project by Google.

260

Answer #1

What blocks Ruby, Python to get Javascript V8 speed?

Nothing.

Well, okay: money. (And time, people, resources, but if you have money, you can buy those.)

V8 has a team of brilliant, highly-specialized, highly-experienced (and thus highly-paid) engineers working on it, that have decades of experience (I"m talking individually – collectively it"s more like centuries) in creating high-performance execution engines for dynamic OO languages. They are basically the same people who also created the Sun HotSpot JVM (among many others).

Lars Bak, the lead developer, has been literally working on VMs for 25 years (and all of those VMs have lead up to V8), which is basically his entire (professional) life. Some of the people writing Ruby VMs aren"t even 25 years old.

Are there any Ruby / Python features that are blocking implementation of optimizations (e.g. inline caching) V8 engine has?

Given that at least IronRuby, JRuby, MagLev, MacRuby and Rubinius have either monomorphic (IronRuby) or polymorphic inline caching, the answer is obviously no.

Modern Ruby implementations already do a great deal of optimizations. For example, for certain operations, Rubinius"s Hash class is faster than YARV"s. Now, this doesn"t sound terribly exciting until you realize that Rubinius"s Hash class is implemented in 100% pure Ruby, while YARV"s is implemented in 100% hand-optimized C.

So, at least in some cases, Rubinius can generate better code than GCC!

Or this is rather matter of resources put into the V8 project by Google.

Yes. Not just Google. The lineage of V8"s source code is 25 years old now. The people who are working on V8 also created the Self VM (to this day one of the fastest dynamic OO language execution engines ever created), the Animorphic Smalltalk VM (to this day one of the fastest Smalltalk execution engines ever created), the HotSpot JVM (the fastest JVM ever created, probably the fastest VM period) and OOVM (one of the most efficient Smalltalk VMs ever created).

In fact, Lars Bak, the lead developer of V8, worked on every single one of those, plus a few others.

Javascript Is Equal To JavaScript: Questions

JavaScript

Django Template Variables and Javascript

4 answers

When I render a page using the Django template renderer, I can pass in a dictionary variable containing various values to manipulate them in the page using {{ myVar }}.

Is there a way to access the same variable in Javascript (perhaps using the DOM, I don"t know how Django makes the variables accessible)? I want to be able to lookup details using an AJAX lookup based on the values contained in the variables passed in.

256

Answer #1

The {{variable}} is substituted directly into the HTML. Do a view source; it isn"t a "variable" or anything like it. It"s just rendered text.

Having said that, you can put this kind of substitution into your JavaScript.

<script type="text/javascript"> 
   var a = "{{someDjangoVariable}}";
</script>

This gives you "dynamic" javascript.

log

Python"s equivalent of && (logical-and) in an if-statement

5 answers

delete By delete

Here"s my code:

def front_back(a, b):
  # +++your code here+++
  if len(a) % 2 == 0 && len(b) % 2 == 0:
    return a[:(len(a)/2)] + b[:(len(b)/2)] + a[(len(a)/2):] + b[(len(b)/2):] 
  else:
    #todo! Not yet done. :P
  return

I"m getting an error in the IF conditional.
What am I doing wrong?

934

Answer #1

You would want and instead of &&.

934

Answer #2

Python uses and and or conditionals.

i.e.

if foo == "abc" and bar == "bac" or zoo == "123":
  # do something

log

How do you get the logical xor of two variables in Python?

5 answers

Zach Hirsch By Zach Hirsch

How do you get the logical xor of two variables in Python?

For example, I have two variables that I expect to be strings. I want to test that only one of them contains a True value (is not None or the empty string):

str1 = raw_input("Enter string one:")
str2 = raw_input("Enter string two:")
if logical_xor(str1, str2):
    print "ok"
else:
    print "bad"

The ^ operator seems to be bitwise, and not defined on all objects:

>>> 1 ^ 1
0
>>> 2 ^ 1
3
>>> "abc" ^ ""
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for ^: "str" and "str"
794

Answer #1

If you"re already normalizing the inputs to booleans, then != is xor.

bool(a) != bool(b)

We hope this article has helped you to resolve the problem. Apart from Javascript Is Equal To, check other JavaScript-related topics.

Want to excel in Python? See our review of the best Python online courses 2022. If you are interested in Data Science, check also how to learn programming in R.

By the way, this material is also available in other languages:



Walter Galleotti

Moscow | 2022-12-03

Thanks for explaining! I was stuck with Javascript Is Equal To for some hours, finally got it done 🤗. Will use it in my bachelor thesis

Walter Gonzalez

New York | 2022-12-03

Simply put and clear. Thank you for sharing. Javascript Is Equal To and other issues with sin was always my weak point 😁. Will use it in my bachelor thesis

Anna Emmerson

Milan | 2022-12-03

JavaScript is always a bit confusing 😭 Javascript Is Equal To is not the only problem I encountered. I am just not quite sure it is the best method

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