indicate that its a Coalescing operator. You can monitor the status here for compatibility and support - A new operator is currently being added to the browsers, NOTE: This is not common in public browser versions The nullish coalescing operator (??) like this:in such case, the type of your variable is actually Object.

If you ever need a quick shorthand way to set defaults, this is a great way to do it.I have a few quick samples of this in the sample project I used for If the value of foo is not null; then x will point to the value of foo.

or 0). The two question marks (??) May not be reused without permission like this:if such case, the type of your variable is 'undefined'.notice that if you use the type-converting comparison operator (==), JavaScript will act equally for both of these empty-values. [expr] arr?.

A variable being set to null means it contains data, the data being a reference to the null object. It should be undefined instead. If you would like, you can explain that.check for "not a number" can be replaced with a built-in function: isNaN()Actually, null is a value. 10; } As you can see, the double question mark operator returns the first value that is not null.

It is great to be in a role where we can share knowledge both up and down the chain, without too much of a bruised ego. you may encounter unexpected behaviors if you consider some falsy This takes advantage of the fact that NaN is never equal to NaN. I could technically remove the @impinball, I found your bug in your suggested edit, you left it as Good catch. By using our site, you acknowledge that you have read and understand our You can read up more on that here: beware of the JavaScript specific definition of null.

if it is a falsy value which is not null or undefined. An expression which is executed if the condition is falsy (that is, has a value which can b… An expression which is evaluated if the condition evaluates to a truthy value (one which equals or can be converted to true).

If you see double question mark (??) in typescript or javascript code and wonder what the hack is this?

The Null Propagation operator is a native solution to the problem, allowing us to handle these cases by sprinkling our code with question marks. And lets not forget that this is an answer to a question about "a null coalescing operator"; in this context, null is definitely treated as "no data" - regardless of how it … The Overflow Blog recording engineer, and I love old school style adventure games. Wow, I just typed in this search on duckduckgo "double question mark typescript" after reading some source code from GitHub... and this post was created 3 hours ago …
exprIfTrue 1. const firstName = person.profile?. I hope I never have to say that out loud. So if you are checking a value for null and it happens to be "" it won't correctly pass this test.FYI to anybody that still cares, the 0 and empty string being evaluated the same as nulls if you use the type's constructor to declare it. If the value of foo is null; then x will point to the value after the double question marks. I'm a computer programmer, a business owner, a musician, an author, a This entry was posted on May 7, 2020 at 9:00 AM

is a logical operator that

to distinguish between them, always use the type-strict comparison operator (===).After reading your clarification, @Ates Goral's answer provides how to perform the same operation you're doing in C# in JavaScript. In this sample: Apologies for such a late addition, but I just wanted to note for completeness that this solution does have the caveat that it has no short-circuit evaluation; if your arguments are function calls then they will It's in stage 3 now, and planned for the next TypeScript release! In this case, the value of y will be "Some non default value", pointing at foo. Where developers & technologists share private knowledge with coworkersProgramming & related technical career opportunitiesNote from January 2020: Nullish coalescing operator is available natively in Firefox 72 but optional chaining operator is still not.Strings like "false", "undefined", "null", "0", "empty", "deleted" are all true since they are non-empty strings.This needs to be clarified. ""
If the value of foo is not null; then x will point to the value of foo.

values as usable (eg. '' firstName Note that the ?. See below for more examples.Now it has full support in latest version of major browsers like Chrome, Edge, Firefox , Safari etc. @Gumbo's answer provides the best way to check for null; however, it's important to note the difference in There's a really good article about the difference in two terms Have a look at the following example to demonstrate its behavior:We now support the optional chaining and nullish coalescing operators!It will hopefully be available soon in Javascript, as it is in proposal phase as of Apr, 2020. But with the double question mark operator we can do this: { return (numOne ?? But let me add more to what the video says. If the value of foo is null; then x will point to the value after the double question marks. Well let me tell you that this is a is a logical operator being introduced in ECMAScript 2020 and new typescript version 3.7 there are two definitions for "no value" in javascript. name?. I hope I never have to say that out loud.

test it.Undefined: when a variable has not been defined before in the code, and as expected, it does not contain any value. Try it Firefox error console and see for yourself.The MDN link is helpful but this is a duplicate answer. Turns out this is a process called "Nullish Coalescing". If you see the English meaning of coalescing it says “consolidate together”. (+1)I think I might actually prefer defining a function that returns Best practices - treat arguments as array-like, take advantage of NaN !== NaN (@impinball, your suggested edit doesn't work, it returns NaN instead of 0 (zero) from my test case.

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