How Can I Effectively Check for Null, Undefined, or Blank Variables in JavaScript?

Checking for Null, Undefined, or Blank Variables in JavaScript

The provided code, isEmpty(val), is a common approach to check for variables that are null, undefined, or have an empty length. However, it may not cover all edge cases.

Using Truthiness Checks

JavaScript employs truthy and falsy values. A variable is considered truthy if it is not explicitly false. This includes non-zero numbers, non-empty strings, objects, and true itself.

Therefore, a simple truthiness check can effectively determine if a variable has a value that is not null, undefined, or blank:

if (value) {
    // Do something...
}

Using typeof Operator

In cases where it's unknown whether a variable even exists (i.e., declared), the typeof operator can be used:

if (typeof foo !== 'undefined') {
    // foo is defined
}

Additional Notes:

• Falsy Values: The list provided in the answer covers all possible falsy values in JavaScript, including null, undefined, NaN, empty strings, 0, and false.
• Truthy Value: A non-empty array is considered a truthy value.
• Property Access: If checking for the existence of a property within an object, use hasOwnProperty() instead of falsiness checks, as some native objects may have falsy properties (e.g., Object.prototype).

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