October 2, 1999 - The null Value

Yehuda Shiran October 2, 1999
The null Value
Tips: October 1999

Yehuda Shiran, Ph.D.
Doc JavaScript

The value null is often used to initialize variables that do not have any special meaning. You can assign it to a variable using the standard assignment statement:

var name = null;

The null value is special in that it is automatically converted to initial values of other data types. When used as a number it becomes 0, when used as a string it becomes "", and when used as a Boolean value it becomes false. Since the source of many JavaScript errors is uninitialized variables, one of the common debugging techniques is to initialize all new variables with a null value.

The JavaScript interpreter uses the null value on two occasions:

  1. Built-in functions return null under certain circumstances.
  2. Non-existent properties evaluate to
    3. null.

When checking for a null value, you should check if it is false:

if (!name) {
}

or if it is null:

if (name == null) {
}