The Best Way to Check for Undefined or Null Variables in JavaScript: What Are the Options?

How to Check for an Undefined or Null Variable in JavaScript?

In JavaScript, checking for undefined or null variables is a common task. One approach involves the use of the following code pattern:

<code class="javascript">if (typeof(some_variable) != 'undefined' && some_variable != null)
{
    // Do something with some_variable
}</code>

However, this approach can be verbose. Some sources suggest a simpler alternative:

<code class="javascript">if (some_variable)
{
    // Do something with some_variable
}</code>

While both approaches aim to achieve the same effect, there is a subtle difference. The second approach is only valid if some_variable has been declared. Otherwise, it will throw a ReferenceError.

Efficient Variation:

The most efficient way to check for null or undefined values is as follows:

<code class="javascript">if ( some_variable === null ){
  // some_variable is either null or undefined
}</code>

Note 1:

This shortened variant requires some_variable to be declared. Otherwise, a ReferenceError will occur. This assumption is often valid in common use cases, such as checking for optional arguments or properties on existing objects.

Note 2:

Note 3:

In general, it's recommended to use === for strict equality checks. However, the proposed solution is an exception. The JSHint syntax checker allows eqnull as an exception for this purpose.

The above is the detailed content of The Best Way to Check for Undefined or Null Variables in JavaScript: What Are the Options?. For more information, please follow other related articles on the PHP Chinese website!