Chapter 14. 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.

Live Code

<!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>

Note

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 just 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. Below, we use the === operator to specifically verify that we are dealing with a null value.

Live Code

<!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>

Note

When verifying a null value, always use === because == does not distinguish between null and undefined.

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