function GetAllListItems() {
        $.ajax
            ({
                url: _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getByTitle('List Name')/items?$select=Title,LinkFilename",
                type: "GET",
                headers:
            {
                "Accept": "application/json;odata=verbose"
            },
                success: function (data, status, xhr) {
                    var dataresults = data.d.results;
                    for (var i = 0; i < dataresults.length; i++) {
                        alert(dataresults[i]["LinkFilename"]);
                    }
                },
                error: function (xhr, status, error) {
                }
            });
    }


    var limit = 3;
    $('input.single-checkbox').on('change', function(evt) {
       if($(this).siblings(':checked').length >= limit) {
           this.checked = false;
       }
    });

       <div class="pricing-levels-3">
          <p><strong>Which level would you like? (Select 3 Levels)</strong></p>
          <input class="single-checkbox"type="checkbox" name="vehicle" value="Bike">Level 1<br>
          <input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 2<br>
          <input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 3<br>
          <input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 4<br>
          <input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 5<br>
          <input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 6<br>
          <input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 7<br>
        </div>