（5）对象里的属性求和
var result = [ { subject: 'math', score: 10 }, { subject: 'chinese', score: 20 }, { subject: 'english', score: 30 } ]; var sum = result.reduce(function(prev, cur) { return cur.score + prev; }, 0); console.log(sum) //60
（6）将[1,3,1,4]转为数字1314
function addDigitValue(prev,curr,curIndex,array){ var exponent = (array.length -1) -curIndex; var digitValue = curr*Math.pow(10,exponent); return prev + digitValue; } var arr6 = [1,3,1,4]; var result7 = arr6.reduce(addDigitValue,0) console.info('result7',result7)