This question already has answers here:
Is it possible to implement equal operator in ES6?
(1 answer)
How to make comparison of objects `a == b` to be true? [duplicate]
(2 answers)
Javascript: operator overloading
(9 answers)
Closed 8 months ago.
I was wondering, if there are any ways on how to compare 2 custom string objects which are instances of classes which extend String, using == doesn't work and it always returns false.
I have tried using valueOf but with no luck, the method gets never called if both operands are objects.
See an example below
class MyString extends String {
doSomething(someData) {
return doSomethingWithData(this, someData);
};
valueOf() {
console.log('valueOf called');
return this.toString();
};
};
When doing console.log(new MyString('hi') == 'hi');, I Get
valueOf called
true
But When doing console.log(new MyString('hi') == new MyString('hi'));, I Get false.
So, the valueOf gets never called and the comparison blindly returns false, is there any possible way to fix it?
Related
This question already has answers here:
How to determine equality for two JavaScript objects?
(82 answers)
Why is `Object() === new Object()` equal to `false`? [duplicate]
(1 answer)
Closed 3 years ago.
I have a variable defined as:
var o = new String("0");
In console when i write:
o === o
it returns true
but when i write:
new String("0") === new String("0")
it returns false
I don't understand why is it working on variable references but not on objects?
I tried it as:
(new String("0")) === (new String("0"))
because the problem may arise due to operator precedence, but it still returns false
new String("0") === new String("0")
Here you are comparing two different Strings having different references. Thats why you are getting false.
o === o
Here, You are actually comparing the same string (reference is same in this case).
This question already has answers here:
Object comparison in JavaScript [duplicate]
(10 answers)
Closed 4 years ago.
When you comparing object with another object with same property why it returns false?
For Example
var person={
age:30
}
var person2={
age:40
}
console.log(person==person) or console.log(person===person)
it show's in console false why?
Objects are reference types, which means the equality operators operate on a reference to the object in memory, not to its contents.
In your particular case, you could serialize the object to a string and then check
const compareSerializableObjects = (a, b) =>
JSON.stringify(a) === JSON.stringify(b)
person === person will always return true as you are comparing the same reference, and if you are comparing person === person2 then it is a different refference which is false.
Did you mean person.age === person2.age ?
This question already has answers here:
Object comparison in JavaScript [duplicate]
(10 answers)
Closed 7 years ago.
I'm trying to manipulate the view of a web messaging system and the default view is a blank object, {}. I used an ng-show="data.currentView == {}" in my AngularJS script to check if it is currently the default view, but it never showed. Then I tried this in my Javascript Console in Chrome:
var data = {}
console.log(data == {})
//Logs false
console.log(data === {})
//Logs false
Why is that statement returning false?
You are testing to see if two objects are the same object, not if they are identical objects.
See the specification:
If Type(x) is the same as Type(y), then … Return true if x and y refer to the same object. Otherwise, return false.
You are comparing references with objects, so they are never equal. A good way would be:
Object.keys(data.currentView).length == 0
This question already has answers here:
Why are two identical objects not equal to each other?
(9 answers)
Closed 8 years ago.
Why {} == {} and {} === {} is false in javascript?
{} == {} // false
{} === {} // false
javascript compares objects by identity, not value. Each object, each {} is distinct.
Same applies to arrays, too.
1) The reason for this is that internally JavaScript actually has two different approaches for testing equality. Primitives like strings and numbers are compared by their value, while objects like arrays, dates, and plain objects are compared by their reference. That comparison by reference basically checks to see if the objects given refer to the same location in memory.so
{} == {} is false
2) it does not make any difference whether you use == or === for comparing objects, because comparing them always returns false.
This question already has answers here:
Why are two identical objects not equal to each other?
(9 answers)
Closed 3 years ago.
I was writing a script, and I had something like
var myObject = {};
if (myObject == {}){
...
}
I was surprised to find that this evaluated to false.
My own findings
Reading up on some of the funny querks javascript does, I found this article, which tells that {} will result in a "truthy" object in an if statement, for example
if ({}){ // true
...
}
Hm, well further ready discuesses String Equality, which for object comparison, says it will return true if they reference the same object. (Even {} === {} returns false)
The only reason I can think that is would return false is that the objects are technically at different memory address, and thus considered different objects.
Because every {} creates a unique object. You can't compare them that way.