var displayString = ""; var arr = [0, 1, 2, 3, 4]; displayString += "not use initialValue: "; arr.reduce(function(acc, idx) { displayString += idx + " "; }); $('#display').text(displayString); displayString = "use initialValue: "; arr.reduce(function(acc, idx) { displayString += idx + " "; }, 0); $('#display2').text(displayString);
<div id="display"></div> <div id="display2"></div>