Is there a "null coalescing" operator in JavaScript?
Is there a null coalescing operator in Javascript?
For example, in C#, I can do this:
String someString = null;
var whatIWant = someString ?? "Cookies!";
The best approximation I can figure out for Javascript is using the conditional operator:
var someString = null;
var whatIWant = someString ? someString : 'Cookies!';
Which is sorta icky IMHO. Can I do better?
The JavaScript equivalent of the C# null coalescing operator ( ?? ) is using a logical OR ( || ):
var whatIWant = someString || "Cookies!";
There are cases (clarified below) that the behaviour won't match that of C#, but this is the general, terse way of assigning default/alternative values in JavaScript.
Clarification
Regardless of the type of the first operand, if casting it to a Boolean results in false , the assignment will use the second operand. Beware of all the cases below:
alert(Boolean(null)); // false
alert(Boolean(undefined)); // false
alert(Boolean(0)); // false
alert(Boolean("")); // false
alert(Boolean("false")); // true -- gotcha! :)
This means:
var whatIWant = null || new ShinyObject(); // is a new shiny object
var whatIWant = undefined || "well defined"; // is "well defined"
var whatIWant = 0 || 42; // is 42
var whatIWant = "" || "a million bucks"; // is "a million bucks"
var whatIWant = "false" || "no way"; // is "false"
function coalesce() {
var len = arguments.length;
for (var i=0; i<len; i++) {
if (arguments[i] !== null && arguments[i] !== undefined) {
return arguments[i];
}
}
return null;
}
var xyz = {};
xyz.val = coalesce(null, undefined, xyz.val, 5);
// xyz.val now contains 5
this solution works like the SQL coalesce function, it accepts any number of arguments, and returns null if none of them have a value. It behaves like the C# ?? operator in the sense that "", false, and 0 are considered NOT NULL and therefore count as actual values. If you come from a .net background, this will be the most natural feeling solution.
If || as a replacement of C#'s ?? isn't good enough in your case, because it swallows empty strings and zeros, you can always write your own function:
function $N(value, ifnull) {
if (value === null || value === undefined)
return ifnull;
return value;
}
var whatIWant = $N(someString, 'Cookies!');
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