var TEST = function () {  
    
    let _savePair;
    
    function _compareAndUpdate(newPair) {
        let newLen = newPair[1] - newPair[0] + 1;
        if (newLen > _savePair.len) {
            _savePair.pair = newPair;
            _savePair.len = newLen;
        }
    }
    
    return {
        exec: function (str) {
            let len = str ? str.length : 0;
            if (!len) { return ''; }
            
            _savePair = { pair: [0, 0], len: 1 };
			let record = {};
            let contPair = [0, 0];
            
            record[str[0]] = 0;
            for (let i = 1; i < len; ++i) {
                let theChar = str[i];
                if (contPair[0] <= record[theChar]) {
                    _compareAndUpdate([ contPair[0], i - 1 ]);
                    contPair[0] = record[theChar] + 1;
                }
                contPair[1] = i;
                record[theChar] = i;
            }
            _compareAndUpdate(contPair);
            
            return str.substr(_savePair.pair[0], _savePair.pair[1]+1);
        }
    };
}();