Javascript: .push is not a function

Question

I am having a problem with my code:

var arrays = [[1, 2, 3], [4, 5], [6]];
console.log(reduce(arrays,function(array,b){
  return array.push(b);
}));

function reduce(array,combine){
  var current = [];
  for(var i = 0;i<array.length;i += 1){
    current = combine(current,array[i]);
  }
  return current;
}
console.log(reduce([1, 2, 3, 4], function(array, b) {
  return array.push(b);
}));

// → [1, 2, 3, 4, 5, 6]

I get this error:

TypeError: array.push is not a function (line 3) 

As far as I understand, this is because it is treating the array argument as something other than an array. However, I thought I fed it the variable "current" which is an array. Can someone explain the problem? Thanks.

Answer 1

Array.push doesn't return an array. It returns the new length of the array it was called on.

So, your return array.push(b); returns an int. That int gets passed back as array... which is not an array so it doesn't have a .push() method.

You need to do:

array.push(b);
return array;