How Can I Reliably Check for Null, Undefined, and Empty Variables in JavaScript?

Check for Null, Undefined, and Blank Variables in JavaScript

When working with JavaScript, it's crucial to determine if variables contain valid data or if they are considered empty or null. A common challenge arises in finding a comprehensive method to verify this across various scenarios.

The provided code snippet:

function isEmpty(val){
    return (val === undefined || val == null || val.length <= 0) ? true : false;
}

attempts to address this issue by checking for undefined, null, and empty strings. However, it's not entirely exhaustive.

A more reliable approach involves assessing whether a variable has a "truthy" or "falsy" value. Truthiness in JavaScript refers to values that are considered true in logical contexts, while falsiness denotes values that evaluate to false.

The following code demonstrates this:

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

Here, the "if" statement will evaluate to true if "value" is not null, undefined, NaN, an empty string, 0, or false. These values represent all possible falsy scenarios in JavaScript.

Additionally, if you're unsure whether a variable exists (i.e., declared), the "typeof" operator can be employed:

if (typeof foo !== 'undefined') {
    // Foo could get resolved and is defined
}

In this case, "foo" is first checked for its existence, ensuring that it has been declared. If it exists, it's subsequently assessed for truthiness.

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