Basic Emulated Logic Gates

This package exports JavaScript classes that can be used to create and connect objects that simulate basic Boolean operations.

• 1. Example Usage
• 2. API
  • 2.1. class TruthTableGate
    • 2.1.1. constructor
    • 2.1.2. method set()
    • 2.1.3. method on()
    • 2.1.4. method evaluate()
  • 2.2. class NotGate
  • 2.3. class AndGate
  • 2.4. class OrGate
  • 2.5. class NandGate
  • 2.6. class NorGate
  • 2.7. class XorGate
• 3. Building Composite Gates

1. Example Usage

const { AndGate } = require("@jhtrauntvein/basic-logic-gates");
const gate = new AndGate();
gate.on((value, channel) => {
   console.log(`output ${channel} value is ${value}`);
});
gate.set(true, 0);
console.log(`output value is ${gate.evaluate()[0]}`);

2. API

2.1. class TruthTableGate

This class is the class from which all other basic gates are derived. It evaluates a boolean function by searching a provided truth table for values that match its current input. It caches the most recent input values so that the logic function can be evaluated at any time.

2.1.1. constructor

This class requires a single argument passed as an array of objects that convey the truth table entries that will be used by the gate. Each object in this array must have the following properties:

• inputs (boolean[], required): specifies the collection of boolean values that will be matched during evaluation. Each argument in the truth table array must have the same number of elements and must not be empty.
• outputs (boolean[], required): specifies an array of one or more boolean values that will be the result for the given set of inputs. All basic gates have only one output channels but composed objects may have multiple outputs. Each entry in the truth table array must have the same number of outputs and must not be empty.

2.1.2. method set()

This method sets the logical value of one of the input channels. If the input value is actually changed, the logical function will be evaluated and its results will be reported to any handlers that have been registered with the on() method. This function requires the following parameters:

• value (boolean, required): specifies the assigned value for the input channel
• channel (number, required): specifies the index of the input value to be set.

This method will return the output vector for the matching truth table entry.

2.1.3. method on()

This method allows the application to register and event handler function that will be invoked any time one of the input channel values have been changed. It supports the following parameters:

• handler (function(value, channel, gate), required): specifies a callback function that will be registered for the given output channel. This function will be called by the gate any time one of its input values have been set and changed. This function will be passed the following parameters:
  • value (boolean): reports the value of the output channel
  • channel (number): reports the output channel index (usually zero)
  • gate (TruthTableGate): reports the gate that is posting this event.
• channel (number, optional): optionally specifies the output channel index on which the handler will be registered. If not specified, this value will default to zero.

2.1.4. method evaluate()

This method may be called at any time to evaluate the gate function based upon the current, cached values in the input channels. Its return value will be the output vector for the entry that matches the current set of inputs.

2.2. class NotGate

The NotGate class extends class TruthTableGate and is the simplest of all of the basic gates. It has a single input channel and a single output channel that evaluates to the logical complement of its input.

2.3. class AndGate

The AndGate class extends class TruthTableGate and has two input channels and a signle output channel that evaluates to the logical AND operator.

2.4. class OrGate

The OrGate class extends class TruthTableGate, has two input channels, and a single output channel that evaluates to the logical OR operator.

2.5. class NandGate

The NandGate class extends class TruthTableGate, has two input channels, and a single output channel that evaluates to the logical Not(And) operator.

2.6. class NorGate

The NorGate class extends class TruthTableGate, has two input channels, and a single output channel that evaluates to the logical Not(Or) operator.

2.7. class XorGate

The XorGate class extends class TruthTableGate, has two input channels, and a single output channel that evaluates to the logical XOR operator. This means that it is asserted only when one, but not both, of its input channels are asserted.

3. Building Composite Gates

More complex logical function gates can be constructed by creating an object that composes basic gates and "wires" inputs to outputs of composed gate components. Such a class should not extend class TruthTableGate but rather should provide its own methods that call the methods of the composed gates. In order to function, a composite gate object must override the set(), on(), and evaluate() functions. The following example declares a four input AND gate:

class AndGate4 {
   #input_gates;
   #output_gate;

   constructor() {
      this.#input_gates = [ new AndGate(), new AndGate() ];
      this.#output_gate = new AndGate();
      this.#input_gates.forEach((gate, gate_idx) => {
         gate.on((value) => this.#output_gate.set(value, gate_idx));
      });
   }

   set(value, channel) {
      if(channel <= 1)
         this.#input_gates[0].set(value, channel);
      else
         this.input_gates[1].set(value, Math.floor(channel / 2));
   }

   on(handler, channel) {
      this.#output_gate.on(handler, channel);
   }
}