How does the || Operator Handle Non-Boolean Operands and Why?

Handling Non-Boolean Operands with the || Operator in JavaScript

The logical OR (||) operator in JavaScript not only evaluates Boolean expressions but also functions with non-Boolean operands. This behavior may seem counterintuitive, but it has a specific purpose known as the "Default Operator."

In JavaScript, || acts as a default operator. When the first operand is a falsy value (e.g., false, null, undefined, empty string, or 0), the operator returns the second operand as the default value. Conversely, if the first operand is truthy (e.g., true, a non-empty string, or a non-zero number), the first operand is returned as the default value.

This functionality is evident in the example provided:

<code class="javascript">var $time = Date.now || function() {
  return +new Date;
};</code>

In this code, if the global Date.now function is not available (falsy), the function provided as the second operand is used as a default fallback to provide the current time. This technique is commonly employed in library code to ensure compatibility across different environments.

To summarize, the || operator in JavaScript serves as both a logical operator (evaluating Boolean expressions) and a default operator (returning a default value for non-Boolean operands). This dual functionality enhances flexibility and allows for convenient handling of various scenarios in JavaScript code.

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