In JavaScript, there are two equality operators: the loose equality operator (==
) and the strict equality operator (===
). The main difference between them is that the loose equality operator performs type coercion before comparing the values, while the strict equality operator compares both the values and their types without any type coercion.
In terms of performance, using the strict equality operator (===
) is generally faster than using the loose equality operator (==
). This is because the strict equality operator does not perform type coercion, which can be an additional overhead.
Here's an example to illustrate the difference:
console.log(1 == '1');
console.log(1 === '1');
In the first comparison (1 == '1'
), the loose equality operator coerces the string '1'
to a number before comparing it with the number 1
. This type coercion takes some time, although it may be negligible in most cases.
In the second comparison (1 === '1'
), the strict equality operator directly compares the number 1
with the string '1'
without any type coercion. Since their types are different, the comparison returns false
.
When comparing values of the same type, both ==
and ===
will have similar performance. However, using ===
is still recommended as it avoids unexpected type coercion and promotes more precise comparisons.
In your example, idSele_UNVEHtype.value.length === 0
is preferred over idSele_UNVEHtype.value.length == 0
because it explicitly compares the length with the number 0
without any type coercion.
While the performance difference between ==
and ===
may not be significant in most cases, using ===
is considered a good practice for several reasons:
- It promotes code clarity and reduces the chances of unexpected behavior due to type coercion.
- It catches potential bugs early by ensuring that the compared values have the same type.
- It aligns with the principle of "explicit is better than implicit," making the code more maintainable and easier to understand.
Therefore, it is generally recommended to use the strict equality operator (===
) for comparisons in JavaScript, unless you specifically need the type coercion behavior of the loose equality operator (==
).