what is the reduce.function(a,b) and after the curly why there 0)?? from last 6 lines

Question

function main() {
//take the number of passed levels
var levels = parseInt(readLine(),10);
var points = new Array();

var count = 0;
while(count<levels){
var elem = parseInt(readLine(),10);
points[count] = elem;
count++;
}

var sum = 0;
sum=points.reduce(function(a,b){
return a+b;
},0);
//calculate the sum of points

//output
console.log(sum);
}

Answer 1

reduce is like knitting.
you hava a list of numbers and get them together one after the other. In your case u get them together by a+b
But how to treat the first number? Well... the first number is joined with 0 (thats what 0 is for)

now lets have a list
1,2,3

reduce does it number by number
the start is 0
0+1 = 1
now 2
1+2 = 3
now 3
3+3 = 6

the result is 6.

now try to multiply all that numbers. Which is start and how to redefine the function?

Answer 2

Thanks