JavaScript code that makes a function run as a parameter of another function_javascript skills

Let’s look at a piece of code first:

Copy the code The code is 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 and sum the elements of the array
alert(map(function(x,y){return x y;}, a , "")) //Connect the elements of the array

The map function defines a traversal of the a array once, but the specific operation to be performed on each element is not defined and needs to be defined from its first parameter.

This approach can improve code reusability. good.