JavaScript Succinctly®
CHAPTER 7
Null
Conceptual overview of using the null value
You can use null to explicitly indicate that an object property does not contain a value. Typically, if a property is set up to contain a value, but the value is not available for some reason, the value null should be used to indicate that the reference property has an empty value.
Sample: sample60.html
<!DOCTYPE html><html lang="en"><body><script> // The property foo is waiting for a value, so we set its initial value to null. var myObjectObject = { foo: null }; console.log(myObjectObject.foo); // Logs 'null'. </script></body></html> |
Notes
Don't confuse null with undefined. undefined is used by JavaScript to tell you that something is missing. null is provided so you can determine when a value is expected but not available yet.
typeof returns null values as "object"
For a variable that has a value of null, the typeof operator returns "object”. If you need to verify a null value, the ideal solution would be to see if the value you are after is equal to null. In the following sample, we use the === operator to specifically verify that we are dealing with a null value.
Sample: sample61.html
<!DOCTYPE html><html lang="en"><body><script> var myObject = null; console.log(typeof myObject); // Logs 'object', not exactly helpful. console.log(myObject === null); // Logs true, only for a real null value. </script></body></html> |
Notes
When verifying a null value, always use === because == does not distinguish between null and undefined.
- 80+ high-performance, responsive JavaScript UI controls.
- Popular controls like DataGrid, Charts, and Scheduler.
- Stunning built-in themes.
- Lightweight and user-friendly.