The difference between || and ?? operators in Javascript & NodeJS
In short, the difference between the two operators boils down to the difference between falsy and null/undefined. Where the logical or (|| ) operator takes the right operand in the case of a falsy value — which includes empty string, 0, false, NaN, etc. The nullish coalescing operator (?? ) takes the right operand only when the left side is set to null or undefined . Having said that, we could think of the ?? operator as subset of the || .
A practical example of where we would want to use the ?? as opposed to the || would be when an empty string "" is a valid value and we want the default value to N/A. Without the ??we would need to write:
if(currentDescription == null) {
targetDescriptionn = "N/A";
}
else {
targetDescriptionn = currentDescription;
}// or using the ternary operatortargetDescription = currentDescription == null ? "N/A": currentDescription
which can be replaced with a shorter one-liner:
targetDescriptionn = currentDescription ?? "N/A"The way I double-check any Javascript behavior I’m unsure about (we all know that javascript doesn’t always behave the way we expect) is by running the interactive nodejs shell. In my experience, it’s a quicker way than googling for an answer. The way to access NodeJS interactive shell is by simply typing node in the terminal (assuming the nodejs is added in the $PATH).
Additional operators — logical AND (&&=) and OR(||=) assignment operators
Logical AND & OR assignment operators are only available in NodeJS version 15+
A nice addition to the above operator is logical AND assignment (&&=) — which behaves very similar to the additional assignment operator (+=). A great use-case of the operator is setting default values on an existing variable.
description &&= "N/A"As already discussed in the previous section, the value of the description will be set to N/A only in the case the description variable is set to null or undefined.
Again, if however, the requirement is to change the value of the description in case of falsy value (let say, empty string) the logical OR assignment (||=) could be used
description ||= "N/A"
