Multiply Array Elements javascript

Question

I have an Array of numbers: var arr = [1,2,3,4,5] I want to get a list like this: input_1 = 1, input_2 = input_1 * 2, input_3= input_2 * 4 .. With me can i do in javascript?

Are you asking for ["variable" variables](https://stackoverflow.com/questions/5187530/variable-variables-in-javascript) or just how to convert this array into another? — VLAZ, Jun 15 '21 at 17:13
If you want a variable for every element in your array dynamically, that's not possible without `eval` or similar. — MinusFour, Jun 15 '21 at 17:36
You can do simple for loop with Object.defineProperty like in below psudo code. function creareVariables (array){ let parent =this;array.forEach((el,idx)=>{if(!idx){Object.defineProperty(parent,'input_'+idx, {value:el})} else{ Object.defineProperty(parent, 'input_'+idx,{value:parent['input_'+(idx-1)]*el})}})} warning untested code.. sent from mobile — Karthikeyan, Jun 15 '21 at 18:21

score 0 · Answer 1 · answered Jun 15 '21 at 17:30

0

Try

var output = {};

arr.forEach((item, i) => {
    output[i+1] = i === 0 ? 1 : (output[i] * (i * 2));
});

Output

{1: 1, 2: 2, 3: 8, 4: 48, 5: 384}

answered Jun 15 '21 at 17:30

Vishnudev Krishnadas

10,679
2
23
55

score 0 · Answer 2 · answered Jun 15 '21 at 17:37

You just need to keep track of the last calculated value and multiply it by the current element. There are lots of different ways to do that, here is one:

var arr = [1,2,3,4,5];

let last = 1;
const output = arr.map(el => last *= el);
console.log(output);

score 0 · Answer 3 · answered Jun 15 '21 at 18:04

Here is a more functional-like implementation using the reduce method (Doc).

var arr = [1,2,3,4,5];

const result = arr.reduce(
  (resultArr, _, i) => {
    if (i === 0) {
      // base case:
      return [1];
    } else {
      // step case:
      return [
        ...resultArr,
        resultArr[resultArr.length - 1] * (2 ** i),
      ];
    }
  },
  [],
);

console.log(result);

Multiply Array Elements javascript

3 Answers3