What is the Non-boolean Behavior of the || Operator?

Understanding the Non-boolean Behavior of the || Operator

The || (logical OR, double vertical line) operator is a versatile tool in programming, but its behavior can be surprising when working with non-boolean operands.

In the example provided:

var $time = Date.now || function() {
  return +new Date;
};

the || operator is not being used for its typical boolean evaluation. Instead, it acts as a "default" operator, assigning the value of the Date.now function to $time if it exists, and falling back to the anonymous function that returns the current time as a numeric value.

This behavior stems from the fact that the || operator evaluates to the first operand if it is truthy (not false, null, undefined, the empty string, or the number 0). If the first operand is falsy, it evaluates to the second operand.

In JavaScript, arrays and objects are considered truthy values, even though they are not boolean data types. This allows the || operator to function as a convenient way to provide default values for non-boolean operands.

For example:

var array1 = [] || [1, 2, 3]; // array1 will be assigned [1, 2, 3]
var object1 = {} || { name: "John Doe" }; // object1 will be assigned { name: "John Doe" }

Understanding the non-boolean behavior of the || operator is crucial for effectively utilizing it in JavaScript code. By leveraging its "default" operator functionality, developers can easily assign default values to non-boolean variables and ensure graceful handling of missing or falsy data.

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