I would like to know the difference between the two operators that would be:
(1): ==
(2): ===
If possible, I would also like to understand the use of their opposite operators in this case:
(3): !=
(4): !==
What would be the difference between the operators:
1:
if (foo == "foo")
2:
if (foo === "foo")
And what would be the difference between opposing operators:
3:
if (foo !== "foo")
4:
if (foo != "foo")
Could anyone tell me?
The difference is that if you use == there will be a coercion of the value so that both sides of the expression have the same type.
In the case of === there will be no coercion and so the code below will give false:
if(1 === '1')
console.log('igual');
else
console.log('diferente');//Esta será a resposta
If we only use == , there will be a coercion so that both are the same type and equal.
if(1 == '1')
console.log('igual');//Esta será a resposta
else
console.log('diferente');
Another example:
if(0 == '')
console.log('igual');//Esta será a resposta
else
console.log('diferente');
In case '' is considered a falsey value, which can be considered false even if it does not have the false value.
In the case below the correct message is given, which are different:
if(0 === '')
console.log('igual');
else
console.log('diferente');//Esta será a resposta
Edited
Here are some other values that can result in strange cases in logical comparison in javascript :
They give false:
0
''
' '
null
undefined
NaN
== makes value-only comparison
=== does value and type comparison
if (1 == "1") // retorna true
if (1 === "1") // retorna false
Same thing with =! and ==! only the command is negation, returns true if the value is different and / or the type is also different.
if (1 != "1") // retorna false
if (1 !== "1") // retorna true
The difference is that the value type is checked.
Ex:
var foo = "10";
console.log(foo == "10"); //true
console.log(foo === 10); //false
== tests if it is equal to === tests if it is equal and of the same type