如何将每个数字与之前的数字相加（JavaScript）？

Question

I have this array of numbers in JS code:

var arrOf12Numbers = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120];

I need to sum the each number with the numbers before.

var cumulative12ArrOfNumbers = [10, 30, 60, 100, 150, 210, etc to 11 index... ];

What is the best way to do that in JS?

UPD : I'm newbie in JS

Answer 1

You could use Array#map and return the sum of the item and the last sum.

This proposal does not alter the original array.

 var array = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120], result = array.map(function (a) { return this.last += a; }, { last: 0 }); console.log(result);

A version without thisArg and a closure

 var array = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120], result = array.map(function (last) { return function (a) { return last += a; }; }(0)); console.log(result);

ES6

 var array = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120], result = array.map((last => a => last += a)(0)); console.log(result);

Answer 2

Simple and fast solution using a regular for loop(without any functions):

 var arrOf12Numbers = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120]; for (var i = 0, len = arrOf12Numbers.length; i < len; i++) { if (i > 0) arrOf12Numbers[i] = arrOf12Numbers[i] + arrOf12Numbers[i - 1]; } console.log(arrOf12Numbers);

And it's more than 2 times faster than approach with map() function(if you care about performance)

---

To get result as a new array use the following approach:

 var arrOf12Numbers = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120], result = arrOf12Numbers.slice(); for (var i = 0, len = result.length; i < len; i++) { if (i > 0) result[i] = result[i] + result[i - 1]; } console.log(result);

The second apprroach is still about 2 times faster than map() function approach

Answer 3

This will do the work without altering the original array. You just have to pass your original array to the function.

 var arrOf12Numbers = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120]; var myFunc = function(arrOf12Numbers) { var cumulative12ArrOfNumbers = []; cumulative12ArrOfNumbers[0] = arrOf12Numbers[0]; for(i=1; i<arrOf12Numbers.length; i++) { cumulative12ArrOfNumbers[i] = arrOf12Numbers[i-1] + arrOf12Numbers[i]; } console.log(cumulative12ArrOfNumbers); }; myFunc(arrOf12Numbers);

Answer 4

This might help you.

 var arrOf12Numbers = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120]; var result = []; var sum = 0; arrOf12Numbers.forEach(function (val, key) { sum += val; result.push(sum); }); console.log(result);

Answer 5

var arr = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120];
for (var i = 1; i < arr.length; i++) {
    sum = arr[i] + arr[i-1];
    arr[i] = sum;
}

Answer 6

It's not really so complicated, just a loop;

 var arrOf12Numbers = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120]; var output = [], sum; for (var i = 0; i < arrOf12Numbers.length;i++) { output.push(i === 0 ? arrOf12Numbers[i] : output[i-1] + arrOf12Numbers[i]) } console.log(output);