Charts.js Formatting Y Axis with both Currency and Thousands Separator

I'm new to chart.js, but here's what I had to do to make Billy Moon's answer work with the latest version 2.1.6.

  var data = {
    labels: ["12 AM", "1 AM", "2 AM", "3 AM", "4 AM", "5 AM", "6 AM", "7 AM", "8 AM", "9 AM", "10 AM", "11 AM", "12 PM", "1 PM", "2 PM", "3 PM", "4 PM", "5 PM", "6 PM", "7 PM", "8 PM", "9 PM", "10 PM", "11 PM"],
    datasets: [
      {
        label: "Sales $",
        lineTension: 0,
        backgroundColor: "rgba(143,199,232,0.2)",
        borderColor: "rgba(108,108,108,1)",
        borderWidth: 1,
        pointBackgroundColor: "#535353",
        data: [65, 59, 80, 81, 56, 55, 59, 80, 81, 56, 55, 40, 59, 80, 81, 56, 55, 40, 59, 80, 81, 56, 55, 40]
      }
    ]
  };

  //var myChart =
  new Chart(document.getElementById('sales-summary-today'), {
    type: 'line',
    data: data,
    options: {
      animation: false,
      legend: {display: false},
      maintainAspectRatio: false,
      responsive: true,
      responsiveAnimationDuration: 0,
      scales: {
        yAxes: [{
          ticks: {
            beginAtZero: true,
            callback: function(value, index, values) {
              if(parseInt(value) >= 1000){
                return '$' + value.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
              } else {
                return '$' + value;
              }
            }
          }
        }]
      }
    }
  });

Again, credit goes to Billy Moon's Answer for the label formatting function.

I'm mostly summarizing what others have mentioned, but I think the cleanest solution to this exact (and frequently encountered) question is to utilize the toLocaleString method with USD currency formatting:

return value.toLocaleString("en-US",{style:"currency", currency:"USD"});

This works in all modern browsers. The Mozilla documentation for toLocaleString lists specific browser compatibility and options for other locales, currencies, and formatting types (e.g. percentages).

Note Chart.js Version 2+ (released in April 2016) requires using the callback method for advanced tick formatting:

var chartInstance = new Chart(ctx, {
  type: 'line',
  data: data,
  options: {
     scales: {
       yAxes: [{
         ticks: {
           callback: function(value, index, values) {
             return value.toLocaleString("en-US",{style:"currency", currency:"USD"});
           }
         }
       }]
     }
   }
 });

The syntax if you are using Chart.js Version 1.X would be:

var myLineChart = new Chart(ctx).Line(data, options);
var data = {
  ...
}
var options = {
  scaleLabel: function(label) {
    return value.toLocaleString("en-US",{style:"currency", currency:"USD"});
}

Credit to Perry Tew for referencing the syntax change, and to mfink for the idea to use toLocaleString.