filtered.push is not a function

Question

I am using reduce function and some reason I get an error on the console:

(index):77 Uncaught TypeError: filtered.push is not a function

DispatchedNumber should exist before mapping into Lines array.

function payload(order) {
  return {
    OrderId: order.ORDERID,
    Lines: order.ITEMS.reduce(function(filtered, item) {
      if (item.DispatchedNumber != undefined) {
        var newItem = {
          Qty: item.Qty,
          QtyShipped: item.DispatchedNumber
        }

        filtered.push(newItem);
      }

      return filtered;
    })
  }
}

test = payload({
  "ORDERID": 1233,
  "ITEMS": [
    { Qty: 123, DispatchedNumber: 111 },
    { Qty: 111 },
    { Qty: 444, DispatchedNumber: 555 },
    { Qty: 443, DispatchedNumber: 323 }
  ]
})

Usage:

console.log(JSON.stringify(test, null, 2));

Example: https://jsfiddle.net/j6097w9d/2/

Possible duplicate of [Using the reduce function to return an array](https://stackoverflow.com/questions/35431292/using-the-reduce-function-to-return-an-array) — Luca Kiebel, Apr 24 '18 at 10:30

score 2 · Accepted Answer · answered Apr 24 '18 at 10:25

There was no initial value specified for the accumulator in the reduce function.

Please update to following

order.ITEMS.reduce(function(filtered, item) {
      if (item.DispatchedNumber != undefined) {
        var newItem = {
          Qty: item.Qty,
          QtyShipped: item.DispatchedNumber
        }

        filtered.push(newItem);
      }

      return filtered;
    }, []) // add the empty array (initial value of accumulator)

For reference, Array.reduce

score 0 · Answer 2 · answered Apr 24 '18 at 10:26

Reduce Syntax

arr.reduce(callback[, initialValue])

You need to be initialise your filtered variable into reduce() function.

DEMO

function payload(order) {
  return {
    OrderId: order.ORDERID,
    Lines: order.ITEMS.reduce(function(filtered, item) {
      if (item.DispatchedNumber != undefined) {
        var newItem = {
          Qty: item.Qty,
          QtyShipped: item.DispatchedNumber
        }
        
        filtered.push(newItem);
      }
      
      return filtered;
    },[])
  }
}

var test = payload({
  "ORDERID": 1233,
  "ITEMS": [{ Qty: 123, DispatchedNumber: 111 },{ Qty: 111 },{ Qty: 444, DispatchedNumber: 555 },{ Qty: 443, DispatchedNumber: 323 }]
})


console.log(JSON.stringify(test, null, 2));

.as-console-wrapper {  max-height: 100% !important;  top: 0;}

filtered.push is not a function

2 Answers2