Pad with leading characters js

//use
paddy(12,5);
paddy(2,4,'#')

/**
* @param {string} value
* @param {number} padLen length of the pad
* @param {string} padChar character used for padding
* @return {string} string with pad
*/
function paddy(value, padLen, padChar) {
    var pad_char = isValid(padChar) ? padChar : '0';
    var pad = new Array(1 + padLen).join(pad_char);
    return (pad + value).slice(-pad.length);
}


/**
 * @param  {obj} el
 * @return {boolean} true if the element in input is set
 */
function isValid(el){
    return typeof el !== 'undefined' && el !== undefined && el !== null && el !== '';
}