js commonly used higher-order functions (filter, map, reduce ...)

let nums = [10,30,50,100,110,300];

1.filter (fn)

Function: Filter, fn is a function that returns a true / false, when retained within the array value is true, otherwise removed

Objective: To screen 100 or less

let nums1 = nums.filter(function(n){

   return n < 100; 

 });

let nums1 = nums.filter(n => n<100)

The results [10,30,50]

2.map（fn）

Function: to carry out fn for each member of the array, the array is returned

Objective: double array value

let nums3 = nums.map(function(n){

   return n*2;

});

let nums3 = nums.map(n => n*10);

The results [100, 300,500,1000,1100,3000]

3.reduce (fn (a, b) {}, the initial value)

功能：类似递归，a为初始值代入，其值返回一个数值c，再次代入fn(a,b),最后得到结果

目的：数组和

let nums4 = nums.reduce(function (pre,n) {

   return n + pre;  

},100);

let nums4 = nums.reduce((m,n) => m+n,100);

结果600