48.reduce排序，去重，取最大值

var arr = [2,4,1,-1,9]
//取最大值
var maxValue = arr.reduce(function(a,b){
    return a>b?a:b
})
console.trace('maxValue->',maxValue)
//数组去重
var arr1 = [2,3,4,5,6,7,4,6,3]
let $arr1 = arr1.reduce(function(prev,number){
    console.log(prev)
    if(prev.indexOf(number)===-1){
        prev.push(number)
    }
    return prev;
 },[])
console.trace('$arr1->',$arr1)
//sort
var arr2 = ["zebras", "dogs", "elephants", "penguins"].sort(function(a, b) {
     return a.length - b.length;
});
console.log(arr2)