Using the reduce function to return an array
I know this is the same answer, but I just want to show that using reduce ()
, the syntax can also be reduced to a single line of code using ES6:
var store = [0,1,2,3,4];
var stored = store.reduce((pV,cV) => [...pV, cV], []);
console.log(stored);
reduce()
can be useful if you need to return an array with multiple items for each item iterated:
var inputs = media.reduce((passedArray, video) => {
passedArray.push("-i");
passedArray.push(video.filepath);
return passedArray;
}, []);
Here it's being used to build the input array for FFmpeg;
[{ name: "bob", filepath: "1.mp4" }, { name: "sue", filepath: "3.mp4" }]
=> ["-i", "1.mp4", "-i", "2.mp4]
Just for completeness, and for the next person who happens on this question, what you're doing is typically achieved with map
which, as stated in the docs
map calls a provided callback function once for each element in an array, in order, and constructs a new array from the results
Contrast that with the description of reduce
:
The reduce() method applies a function against an accumulator and each value of the array (from left-to-right) to reduce it to a single value.
(Emphasis mine) So you see, although you can manipulate reduce
to return a new array, it's general usage is to reduce an array to a single value.
So for your code this would be:
var store = [0,1,2,3,4];
var stored = store.map(function(pV){
console.log("pv: ", pV);
return pV;
});
Much simpler than trying to reconstruct a new array using either push
or concat
within a reduce
function.
push
returns the new length of the array.
What you need is the initially provided array.
So change the code as below.
var store = [0, 1, 2, 3, 4];
var stored = store.reduce(function(pV, cV, cI){
console.log("pv: ", pV);
pV.push(cV);
return pV; // ********* Important ******
}, []);
concat
returns the new array combining the elements of the provided array and concatenated elements. so it works.