If you see double question mark (??) It's a special value of type Object. In other words,

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. numTwo) ?? All Content Copyright 2005-2020 Jeffry Houser. Turns out this is a process called "Nullish Coalescing". Try it Firefox error console and see for yourself.The MDN link is helpful but this is a duplicate answer. @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. I'm a computer programmer, a business owner, a musician, an author, a Coalescing operator returns the first NON-NULL value from a chain. Free 30 Day Trial By using our site, you acknowledge that you have read and understand our Stack Overflow works best with JavaScript enabled 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. "" The two question marks (??) The Overflow Blog if you use || to provide some default value to another variable foo, If you see the English meaning of coalescing it says “consolidate together”. in typescript or javascript code and wonder what the hack is this?

your coworkers to find and share information. values as usable (eg. '' 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 can read up more on that here: beware of the JavaScript specific definition of null. 10; } As you can see, the double question mark operator returns the first value that is not null. Here's the comparison between the null operator and Nullish Coalescing OperatorThanks for contributing an answer to Stack Overflow! If the value of foo is not null; then x will point to the value of foo. You can see this youtube video which demonstrates the whole thing practically. An expression which is executed if the condition is falsy (that is, has a value which can b… or 0). An expression whose value is used as a condition. And by the way, that is a fast way of checking NaNs taking advantage of the fact NaN !== NaN. recording engineer, and I love old school style adventure games. It should be undefined instead. condition 1. 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. I hope I never have to say that out loud. exprIfFalse 1.

indicate that its a Coalescing operator. I find it fascinating when lesser experienced devs on my team do something incredibly awesome that I knew nothing about. null or undefined, and otherwise returns its left-hand side operand.Contrary to the logical OR (||) operator, the left operand is returned

If the value of foo is null; then x will point to the value after the double question marks. if it is a falsy value which is not null or undefined. returns its right-hand side operand when its left-hand side operand is

Featured on Meta In this sample: You should comment under vaughan's answer instead. An expression which is evaluated if the condition evaluates to a truthy value (one which equals or can be converted to true).

[expr] arr?. 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. If you come from a .net background, this will be the most natural feeling solution.If anyone's brain works like mine, and you want to exclude For those who want the code as short as possible, and don't mind a little lack of clarity, you can also use this as suggested by @impinball. The best approximation I can figure out for Javascript is using the conditional operator:The JavaScript equivalent of the C# null coalescing operator (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.Regardless of the type of the first operand, if casting it to a Boolean results in this solution works like the SQL coalesce function, it accepts any number of arguments, and returns null if none of them have a value. A variable being set to null means it contains data, the data being a reference to the null object. firstName Note that the ?. (args) Description. alert(null || '') still alerts an empty string, and I think I actually like that alert('' || 'blah') alerts blah rather than an empty string - good to know though! is a logical operator that