Is it possible to check for null inline in javascript?

Question

I have a function which parses the address components of the Google Maps API JSON and then returns the city / locality / route name.

The getAddressComponent() returns a null if it cannot find the key.

let route = getAddressComponent(addressComponents, 'route').value.long_name;

So let's say it didn't find the key, then I get a Error: TypeError: Cannot read property 'long_name' of undefined obviously because it's not defined.

How do I check for null in javascript other than the conditional method (a === null)?

How can I simply check like this with ?

EDIT : Safe Navigation Operator

let route = getAddressComponent(addressComponents, 'route')?.value.long_name;

And if it doesn't exists, it could probably set route to null instead of throwing a Error ?

Answer 1

2020 Answer, It Exists!!!

You can now directly use ?. inline to test for existence. It is called the Optional Chaining Operator, supported by all modern browsers.

If a property exists, it proceeds to the next check, or returns the value. Any failure will immediately short-circuit and return undefined.

const example = {a: ["first", {b:3}, false]}

example?.a  // ["first", {b:3}, false]
example?.b  // undefined

example?.a?.[0]     // "first"
example?.a?.[1]?.a  // undefined
example?.a?.[1]?.b  // 3

domElement?.parentElement?.children?.[3]?.nextElementSibling

To ensure a default defined value, you can use ??. If you require the first truthy value, you can use ||.

example?.c ?? "c"  // "c"
example?.c || "c"  // "c"

example?.a?.[2] ?? 2  // false
example?.a?.[2] || 2  // 2

If you do not check a case, the left-side property must exist. If not, it will throw an exception.

example?.First         // undefined
example?.First.Second  // Uncaught TypeError: Cannot read property 'Second' of undefined

?. Browser Support - 92%, Dec 2021

?? Browser Support - 92%

Node Support - v14+

Answer 2

Update 2020

This long-wished feature is now available in JavaScript!

I'll redirect to Gibolt's answer, which covers it well.

Original 2018 answer

• There is no "null-safe navigation operator" in Javascript (EcmaScript 5 or 6), like ?. in C#, Angular templates, etc. (also sometimes called Elvis operator, when written ?:) , at least yet, unfortunately.

• You can test for null and return some dependent expression in a single line with the ternary operator ?:, as already given in other answers :

(use === null to check only for nulls values, and == null to check for null and undefined)

    console.log(myVar == null ? myVar.myProp : 'fallBackValue');

• in some cases, like yours, when your variable is supposed to hold an object, you can simply use the fact that any object is truthy whereas null and undefined are falsy values :

    if (myVar) 
        console.log(myVar.myProp)
    else
        console.log('fallbackValue')
  

  You can test for falsy values by coalescing to boolean with !! and make this inline :

    console.log(!!myVar ? myVar.myProp : 'fallbackValue');
  

  Be very careful though with this "falsy test", for if your variable is 0, '', or NaN, then it is falsy as well, even though it is not null/undefined.

Answer 3

Code below simplified return num ? num : 0 for me:

return num || 0;

As of today more correct semantically;

return num ?? 0

Answer 4

let component = getAddressComponent(addressComponents, 'route');
let route = component ? component : null

you can use the ? operator to check the value is true or false then set the value in javascript null will be false