'This' is undefined in es6 class method even if it is defined

Question

this is not available in the methods. More details in my code (comment blocks) about what is available, it's difficult to explain this in plain text. This is probably a duplicate but I don't find a straight answer anywhere.

Is something wrong with this code, or is there a logic workaround?

Class

class CheckParameters {  
    get parameters() {
        return this._parameters;
    }                                                                                                     
    constructor(parameters) {                                                                                                 
        this._parameters = parameters;                                                                                        
        console.log(this);   //this is defined                                                                             
    }                                                                                                                         
                                                                                                                              
    CheckQueryParam (req, res, next) {  
        console.log(this);   // undefined                                                                                      
        let parameterChecks = this._parameters.map(param => { // TypeError: Cannot read property '_parameters' of undefined   
            return new Promise((resolve, reject) => {...});                                                                   
        });                                                                                                                   
        Promise.all(parameterChecks)                                                                                          
            .then(() => next())                                                                                               
            .catch((error) => {                                                                                               
                console.error(error);                                                                                         
                res.status(400).send(error)                                                                                   
            });                                                                                                               
    }                                                                                                                         
}

Using the class

console.log(LimitAndOffset.parameters); //Also this is defined

const LimitAndOffset = new CheckParameters([ 
    new Parameter(    //Parameter is another class, this works perfectly                       
        "limit",                             
        Number,                              
        [Validators.Number],                 
        true                                 
    ),                                       
    new Parameter(                           
        "offset",                            
        Number,                              
        [Validators.Number],                 
        true                                 
    )                                        
]);  

app.get('/', LimitAndOffset.CheckQueryParam, function (req, res) {
    res.status(200).json('piemel');
});