Unique Values from array of objects

From: http://stackoverflow.com/questions/15125920/how-to-get-distinct-values-from-an-array-of-objects-in-javascript#35092559

by Dominic Myers

HTML

<pre id="dates">
    
</pre>

CSS

pre {
    outline: 1px solid #ccc;
    padding: 5px;
    margin: 5px;
}

.string {
    color: green;
}

.number {
    color: darkorange;
}

.boolean {
    color: blue;
}

.null {
    color: magenta;
}

.key {
    color: red;
}

JavaScript

let syntaxHighlight = (json) => json
    .replace(/&/g, '&amp;')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
    .replace(/("(\\u[a-zA-Z0-9]{4}|\\[^u]|[^\\"])*"(\s*:)?|\b(true|false|null)\b|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)/g, (match) => {
        var cls = 'number';
        if (/^"/.test(match)) {
            if (/:$/.test(match)) {
                cls = 'key';
            } else {
                cls = 'string';
            }
        } else if (/true|false/.test(match)) {
            cls = 'boolean';
        } else if (/null/.test(match)) {
            cls = 'null';
        }
        return '<span class="' + cls + '">' + match + '</span>';
    });

let attendance = [{
	"date": "2015-01-07",
	"username": "Others",
	"name": 8,
	"dues": null
}, {
	"date": "2015-01-14",
	"username": "Others",
	"name": 10,
	"dues": null
}, {
	"date": "2015-01-21",
	"username": "Others",
	"name": 9,
	"dues": null
}, {
	"date": "2015-01-28",
	"username": "Others",
	"name": 8,
	"dues": null
}, {
	"date": "2015-02-04",
	"username": "Others",
	"name": 8,
	"dues": null
}, {
	"date": "2015-12-09",
	"username": "Others",
	"name": 9,
	"dues": null
}, {
	"date": "2015-12-16",
	"username": "Others",
	"name": 9,
	"dues": null
}, {
	"date": "2015-12-23",
	"username": "Others",
	"name": 8,
	"dues": null
}, {
	"date": "2015-12-30",
	"username": "Others",
	"name": 7,
	"dues": null
}, {
	"date": "2016-01-13",
	"username": "user1@example.com",
	"name": "Dominic",
	"dues": 1
}, {
	"date": "2016-01-13",
	"username": "user2@example.com",
	"name": "Derek",
	"dues": 1
}, {
	"date": "2016-01-13",
	"username": "user3@example.com",
	"name": "Gemma",
	"dues": 1
}, {
	"date": "2016-01-13",
	"username": "user5@example.com",
	"name": "Chris",
	"dues": 1
}, {
	"date": "2016-01-13",
	"username": "user6+user2@example.com",
	"name": "Jack",
	"dues": 1
}, {
	"date": "2016-01-13",
	"username": "user4@example.com",
	"name": "James",
	"dues": 1
}, {
	"date": "2016-01-13",
	"username":...