I have this code:

isTinyInt: function () {
        var val = $(this).val();
        if (val >= 0 && val <= 255)
            return true;
        else
            return false;
    }



Can I make sure with this that the number is in the tinyint range?

signed or unsigned tinyint?

Your function looks good though it will only work if this is an appropriate DOM elememt.

You might like to consider a generalised int verifier framed as a jQuery plugin :

jQuery.fn.isInSqlIntRange = function (options) {
    var settings = $.extend({
        'type': 'int',
        'unsigned': false
    }, options);
    var min, max, val = this.val();
    if (val === '' || Number(val) === NaN) {
        return false;
    }
    val = Number(val);
    switch (settings.type) {
        case 'tinyint':
            min = settings.unsigned ? 0 : -128;
            max = settings.unsigned ? 255 : 127;
            break;
        case 'smallint':
            min = settings.unsigned ? 0 : -32768;
            max = settings.unsigned ? 65535 : 32767;
            break;
        case 'mediumint':
            min = settings.unsigned ? 0 : -8388608;
            max = settings.unsigned ? 16777215 : 8388607;
            break;
        case 'int':
        case 'integer':
            min = settings.unsigned ? 0 : -2147483648;
            max = settings.unsigned ? 4294967295 : 2147483647;
            break;
        case 'bigint':
            min = settings.unsigned ? 0 : -9223372036854775808;
            max = settings.unsigned ? 18446744073709551615 : 9223372036854775807;
            break;
        default:
            throw typeError('jQuery.isInIntRange() - type is undefined or invalid');
    }
    return val >= min && val <= max;
}

Sample call :

var foo = $("#myInput").isInSqlIntRange({
    'type': 'tinyint',
    'unsigned': true
});

DEMO