Понимание Einsum NumPy

document.getElementById('value').addEventListener('keydown', function(e) {
    var key   = e.keyCode ? e.keyCode : e.which;

/*lenght of value to use with index to know how many numbers after.*/

    var len = $('#value').val().length;
    var index = $('#value').val().indexOf('.');
    if (!( [8, 9, 13, 27, 46, 110, 190].indexOf(key) !== -1 ||
                    (key == 65 && ( e.ctrlKey || e.metaKey  ) ) ||
                    (key >= 35 && key <= 40) ||
                    (key >= 48 && key <= 57 && !(e.shiftKey || e.altKey)) ||
                    (key >= 96 && key <= 105)
            )){
        e.preventDefault();
    }

/*if theres a . count how many and if reachs 2 digits after . it blocks*/ 

    if (index > 0) {
        var CharAfterdot = (len + 1) - index;
        if (CharAfterdot > 3) {

/*permits the backsapce to remove :D could be improved*/

            if (!(key == 8))
            {
                e.preventDefault();
            }

/*blocks if you try to add a new . */

        }else if ( key == 110) {
            e.preventDefault();
        }

/*if you try to add a . and theres no digit yet it adds a 0.*/

    } else if( key == 110&& len==0){
        e.preventDefault();
        $('#value').val('0.');
    }
});