The Nullish Coalescing Operator
1 min read
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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.
The problem
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");If 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 config.respawn:
setAllowedRespawns(config.respawns != null ? config.respawns : "3");This doesn't read very well and is difficult to remember and type.
The solution
A new JavaScript operator called the "Nullish Coalescing Operator" proposes a new syntax for this:
setAllowedRespawns(parameters.respawns ?? "3");If the left-hand side of the expression evaluates to undefined or 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.
Woah! Can I use it?
This feature is currently in stage 1, but is of course available as a babel plugin.
Enjoy!
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