Using the reduce function to return an array

Question

Why is it that when I want to use the push function inside the reduce function to return a new array I get an error. However, when I use the concat method inside the reduce

Answer 1

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]