1 min read
By Erik Wendel
December 8, 2018
Another surprisingly handy new feature proposal
myFunction(somePossiblyNullVariable || "my-default-value");
Does this look familiar?
Providing a default value for when input values are undefined is a very common scenario. Many developers tend to rely on the boolean
OR-operator for this.
This doesn't work when one of the possible values in the left-hand side expression is a so-called falsy value:
""; // an empty string 0; // the number zero false;
setAllowedRespawns(config.respawns || "3");
parameters.respawns is zero, the statement would resolve to the default value, '3'. In fact, you would need a more complex construction to make zero a possible value of
setAllowedRespawns(config.respawns != null ? config.respawns : "3");
This doesn't read very well and is difficult to remember and type.
setAllowedRespawns(parameters.respawns ?? "3");
If the left-hand side of the expression evaluates to
null, the right-hand side of the expression is returned.
The big advantage over
|| is therefore that so-called "falsy" values are passed through as legal values from the left-hand side.
This feature is currently in stage 1, but is of course available as a babel plugin.