Key combination detector (for the Konami Code and otherwise)

key-combo-detector.js

/**
 * Reads sequences of keypresses, then activates a function when a sequential combo has been detected.
 * @author Drake Luce <[email protected]>
 */
class KeyComboDetector {

	/**
	 * Create a key combination detector.
	 * @param {function} functionToCall The function that is called when the combo has been detected.
	 * @param {boolean} [makeListener=true] Make internal listener for keypresses instead of using the detect method.
	 * @param {number[]} [code=[38, 38, 40, 40, 37, 39, 37, 39, 66, 65]] An array of keyCode values representing the sequence of keypresses needed to activate the combo.
	 */
	constructor(functionToCall, makeListener = true, code = [38, 38, 40, 40, 37, 39, 37, 39, 66, 65]){
		this.functionToCall = functionToCall;
		this.code = code;
		this.keysSoFar = [];

		const outerThis = this;
		if(makeListener) window.addEventListener("keyup", function(event){
			outerThis.detect(event);
		});
	}

	/**
	 * Detect a keypress for combo detection.
	 * @param {KeyboardEvent} event The keyboard event from your listener.
	 */
	detect(event){
		const nextKeyIndex = this.keysSoFar.length;
		if (event.keyCode != this.code[nextKeyIndex]) return this.keysSoFar = [];
		this.keysSoFar.push(event.keyCode);
		if(this.keysSoFar.length == this.code.length){
			this.keysSoFar = [];
			this.functionToCall();
		}
	}

	/**
	 * Change the sequence of keys needed to detect the combo. This resets the keys pressed so far.
	 * @param {number[]} code An array of keyCode values representing the sequence of keypresses needed to activate the combo.
	 */
	setCode(code){
		this.code = code;
		this.keysSoFar = [];
	}

	/**
	 * Change the function that is called when the combo has been detected.
	 * @param {function} functionToCall The functon that is called when the combo has been detected.
	 * @param {boolean} [resetKeysPressedSoFar=false] Whether the keys pressed so far should be reset.
	 */
	setFunctionToCall(functionToCall, resetKeysPressedSoFar = false){
		this.functionToCall = functionToCall;
		if (resetKeysPressedSoFar) this.keysSoFar = [];
	}
}

// Example
const keyComboDetector = new KeyComboDetector(function(){
	console.log("Cheat codes activated!");
});