charCodeSequence

A handy lightweight library that detects that a sequence of characters was pressed in succession. Once the key sequence is detected a callback in invoked.

Usage

const { listenKeypress, konami, findMatchFactory } = require('char-code-sequence');

Supply an array of charCodes to listen for :

const nameArray = [114, 111, 110]; // my name 'ron'
const findNameMatch = listenKeypress(nameArray, () => console.log('boo yah, typed the whole thing.'));
 
// access the current store of typed charCodes
console.log(findNameMatch.currArr);

NOTE* This function works in Node.js - but it's essentially a no-op since no document object exists

Use the findMatchFactory directly :

If you're not running your code in a browser, you can require the findMatchFactory directly to detect a sub-array or substring match

const findMatchFactory = require('char-code-sequence/src/findMatchFactory');
 
let called = 0;
const findMatch = findMatchFactory('sam'.split(''), (currArr) => {
    called++;
    console.log(`found ${currArr.join('')} in the string!`);
});
 
'so sam went to the store sasasam was sad.'.split('').forEach(findMatch);
console.log(called); // 2
 
const findArrMatch = findMatchFactory([1, 2, 3], console.log);
[1, 2, 1, 2, 1, 2, 3, 4].forEach(findArrMatch); // will console.log [1, 2, 3] after the full sequence is used

Add onChange handlers, these will be invoked any time the array changes :

findNameMatch.onChange(({ currArr, event }) => {
    console.log('the keypress event: ', event);
    console.log(currArr.map(code => String.fromCharCode(code)); // 'r', 'o', 'n'
}));

Built in support to listen for the konami code :

charCodeSequence.konami(myCallback); // [up, up, down, down, left, right, left, right, 'b', 'a']

charCodes vs. keyCodes

The listenKeypress function doesn't support listening for characters like letters, etc. Instead you must supply an array of charCodes, that's the code associated with the document event 'keypress.'

Note, this is distinct from the information you get from the 'keydown' event. Try the following in your browser's console :

    document.addEventListener('keydown', e => console.log('keydown', e.which)); // logs the keyCode
    document.addEventListener('keypress', e => console.log('keydown', e.which)); // logs the charCode

The key code corresponds to a key on the keyboard that was pressed, while the charCode corresponds to a unicode character that was typed.

Source: http://www.dotnetfunda.com/forums/show/20870/diffrence-between-keycode-charcode-in-javascript-or-keycode-vs-charcod

So pressing the letter 'a' yeilds a different keyCode than and charCode

'a'.charCodeAt(0); // 97 
document.addEventListener('keydown', e => console.log(e.which)); // user types 'a', outputs 65

Here are a couple resources for discovering which char codes are which :

• https://www.cambiaresearch.com/articles/15/javascript-char-codes-key-codes
• http://unixpapa.com/js/key.html
• http://keycode.info/

Use this key for simple strings (if you want special characters look those up using the links above) :

• 65 - 91 = upper case letters
• 97 - 123 = lower case letters
• to get a corresponding lower case letter from an upper case letter, add 32
• intergers (0 - 9) are in the range from 48 - 57
• space is 32

Proper solution

A naive approach to detecting a sequence is to match each letter in the sequence, and if a mismatch is found, then start over.

However, consider the following cases :

code array = [1, 1, 2, 2]
user input = [1, 1, 1, 2, 2]

code array = [3, 4, 3, 4, 5]
user input = [3, 4, 3, 4, 3, 4, 5]

search string = 'one on one'
user types = 'one one on one'

The previous approach fails for these sequences because after we get to the first mis-matched character everything before is discarded, however the user did type the sequence.

The algorithm in this package efficiently disposes of typed characters that don't match your character code array.

Interesting properties

Coincidentally, the method of matching the end of the input and iteratively discarding characters that don't match produces a highly efficient solution for a sub-array match algorithm. Check out the code example above titled 'Use the findMatchFactory directly.'

You could also use this algorithm in a stream, I've provided a sample of that as well : Stream Sample

Everything is unit tested and beautiful

... If you find a sequence that's not working for some reason, please let me know - but check that you correctly selected your key codes first.