Javascript - 将数组中的元素与其位置相乘

Question

How can I multiply the elements in an array by their positions in the array?

For example,

I want to take the elements in this array

var multiply = [2, 4, 6, 7]

and essentially come out with ( 2*1+4*2+6*3+7*4 ).

I understand that I need to use a for loop but I don't know how to write it to get that result.

Thank you!

Answer 1

Do it like this, but try to understand how it works:
I have replaced the old values in the array.
So multiply changed into the new values in this example.

 var multiply = [2, 4, 6, 7]; multiply.forEach(function(e, i) { multiply[i] = e * ++i; }) document.write(JSON.stringify(multiply)); // output: [2,8,18,28]

Answer 2

You could use the following:

multiply.map(function(v, i){
  return v * (i+1);
});

You can assign it to a variable or do whatever you need with this (since a new array is returned).