Getting day of the week from timestamp using JavaScript

var timestamp = 654524560; // UNIX timestamp in seconds
var xx = new Date();
xx.setTime(timestamp*1000); // javascript timestamps are in milliseconds
document.write(xx.toUTCString());
document.write(xx.getDay()); // the Day

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2020 Update

If this browser support is acceptable for you you can use this one liner:

new Date(<TIMESTAMP>).toLocaleDateString('en-US', { weekday: 'long' }); // e.g. Tuesday

var timestamp = 1400000000;
var a = new Date(timestamp*1000);
var days = ['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'];
var dayOfWeek = days[a.getDay()]

Now the "day of the week" is in the dayOfWeek variable.