Sorting array of objects based on date

That's because your date String can't be parsed as a valid date, you'd need to rearrange the string you are passing to new Date(). For example the following would produce a parsable date:

function rearrangeDate(dateString) {
    var r = dateString.split('/');
  return r[1] + "/" + r[0] + "/" + r[2];
}

which you then can use

function sortRecords (records) {

  var sorted = records.sort(function(a, b){
    return new Date(rearrangeDate(a.date)) - new Date(rearrangeDate(b.date)); 
  });

  return sorted;

}

try this

    let sorted = 
     [{
        date: "26/11/2016",
        hourlyRate: 50,
        hoursWorked: 10,
        name: "Mr G",
        natInsNumber: "GG845893G"
    },
    {
        date: "14/10/2016",
        hourlyRate: 50,
        hoursWorked: 10,
        name: "Mr A",
        natInsNumber: "GG845893G"
    },
    {
        date: "11/09/2016",
        hourlyRate: 50,
        hoursWorked: 10,
        name: "Mr H",
        natInsNumber: "GG845893G"
    },
    {
        date: "26/10/2016",
        hourlyRate: 50,
        hoursWorked: 10,
        name: "Mr L",
        natInsNumber: "GG845893G"
    }
];

function CreateDate(dateString) {
    var arr = dateString.split('/');
    return new Date(arr[2] , arr[1], arr[0]);
}

function sortRecords(records) {    
    var sorted = records.sort(function (a, b) {        
        return CreateDate(a.date) > CreateDate(b.date);
    });
    console.log(sorted);
}

sortRecords(sorted);

Produces below output: