JavaScript code that makes a function run as a parameter to another function _javascript tips

First look at a piece of code:

Copy Code code as follows:

var a = [1,2,3];
function Map (FN, a, init) {
var s = init;
for (i = 0; i < a.length; i++) {
s = fn (s,a[i]);
}
return s;
}
Alert (Map (function (x,y) {return x+y}, a, 0)////Add the elements of an array to sum
Alert (Map (function (x,y) {return x+y;}, A, "")//Connect the elements of an array

The map function defines how an array is traversed once, but does not define what is done with each element, but is defined from its first argument.

This method can improve the reusability of the code. Not bad.