Javascript Reduce Function Not working

Question

I am trying to work with higher order functions, in an attempt to be a better javascript developer.

The error I'm getting from the code below is TypeError: myArray.reduce is not a function I swear I'm following the correct design pattern.

function myFunction(myArray) {
    return myArray.reduce((prev, curr) => prev * curr);
}
var myArray = [3, 2, 3]
var myObject = myFunction.apply(myObject, myArray); // Will each element in array be multiplied?

What browser/version are you using? I know we saw that chrome 44 didn't support => but 47 or 48 did. — klog, Aug 11 '16 at 17:25
@Arnauld I am attempting to work with apply, arrow functions, and reduce patterns. — Chris Clark, Aug 11 '16 at 17:26
@ChrisClark Fair enough. Then you should use `myFunction.apply(myObject, [myArray])` — Arnauld, Aug 11 '16 at 17:28

Goodbye StackExchange · Accepted Answer · 2016-08-11T17:30:20.017

4

You want to use .call instead of .apply.

.call will pass in each object and pass them directly to the function, while .apply will take an array of parameters and pass them in as each separate variable.

You can see the effects below, with this simple script:

function myFunction() {
    console.log(arguments);
}
var myArray = [3, 2, 3];

myFunction.call(null, myArray);
/*
 Will echo out {
   "0": [
    3,
    2,
    3
 ]}
 
 The first variable will contain the entire array
*/

myFunction.apply(null, myArray);
/*
 Will echo out {
  "0": 3,
  "1": 2,
  "2": 3
 }
 
 The first variable will be 3, the second 2, and the third 3
*/

edited Aug 11 '16 at 17:30

answered Aug 11 '16 at 17:26

Goodbye StackExchange

21,680
7
47
83

2

Alternatively, `myFunction.apply(myObject, [myArray])`. – melpomene Aug 11 '16 at 17:27
@ChrisClark more reading -> http://stackoverflow.com/questions/1986896/what-is-the-difference-between-call-and-apply – aw04 Aug 11 '16 at 17:29

score 1 · Answer 2 · answered Aug 11 '16 at 17:33

Instead of using

var myObject = myFunction.apply(myObject, myArray);

Use

var myObject = myFunction.call(myObject, myArray);

Since function.prototype.apply method takes each items of array as a parameter. myArray parameter becomes 3, 2, 3 so It behaves like your function took 3 parameters.

Javascript Reduce Function Not working

2 Answers2