Chart.js Add Commas to Tooltip and Y-Axis

For your yAxes ticks options, this will add commas at the thousands marks:

ticks: {
    beginAtZero:true,
    userCallback: function(value, index, values) {
        value = value.toString();
        value = value.split(/(?=(?:...)*$)/);
        value = value.join(',');
        return value;
    }
}

Similar function can be added in a tooltip callback.

Full example in this FIDDLE

I see a lot of overly complicated answers for this.

This functionality is already built into javascript with .toLocaleString(), we don't have to reinvent to wheel! This accounts for decimals as well.

yAxes: [
    {
        ticks: {
            beginAtZero: true,
            userCallback: function(value, index, values) {
                return value.toLocaleString();   // this is all we need
            }
        }
    }
]