Merge/flatten an array of arrays

Question

I have a JavaScript array like:

[["$6"], ["$12"], ["$25"], ["$25"], ["$18"], ["$22"], ["$10"]]

How would I go about merging the separate inner arrays into one like:

["$6", "$12", "$25", ...]

Answer 1

You can use concat to merge arrays:

var arrays = [
  ["$6"],
  ["$12"],
  ["$25"],
  ["$25"],
  ["$18"],
  ["$22"],
  ["$10"]
];
var merged = [].concat.apply([], arrays);

console.log(merged);

Using the apply method of concat will just take the second parameter as an array, so the last line is identical to this:

var merged2 = [].concat(["$6"], ["$12"], ["$25"], ["$25"], ["$18"], ["$22"], ["$10"]);

---

There is also the Array.prototype.flat() method (introduced in ES2019) which you could use to flatten the arrays, although it is only available in Node.js starting with version 11, and not at all in Internet Explorer.

const arrays = [
      ["$6"],
      ["$12"],
      ["$25"],
      ["$25"],
      ["$18"],
      ["$22"],
      ["$10"]
    ];
const merge3 = arrays.flat(1); //The depth level specifying how deep a nested array structure should be flattened. Defaults to 1.
console.log(merge3);