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4.10 Logical Expressions

In order to understand how the instanceof operator works, you must understand the “prototype chain.” This is JavaScript’s inheritance mechanism, and it is described in §6.2.2 . To evaluate the expression o instanceof f, JavaScript evaluates f.prototype, and then looks for that value in the prototype chain of o. If it finds it, then o is an instance of f (or of a superclass of f) and the operator returns true. If f.prototype is not one of the values in the prototype chain of o, then o is not an instance of f and instanceof returns false.


4.10 Logical Expressions

The logical operators &&, ||, and ! perform Boolean algebra and are often used in conjunction with the relational operators to combine two relational expressions into one more complex expression. These operators are described in the subsections that follow. In order to fully understand them, you may want to review the concept of “truthy” and “falsy” values introduced in §3.3 .

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