在Javascript / NodeJS中串联未知数量的数组

Question

I have a function in one of my controllers where I populate an array of references to a document, which, when populated, have embedded arrays themselves.

Here's an example:

The mongoose populate function gives me an array of objects. Within each of those objects is an array:

[{ name: Test, array: [ 1, 2, 3, 4, 5 ] }, { name: TestAgain, array: [1, 2, 3, 4, 5] }, { name: Test^3, array: [1, 2, 3, 4, 5]}, {...

The desired output would be:

[1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, ...]

I need to concatenate all of the "arrays" within the populated references. How can I do this without knowing how many arrays there are?

For reference, here is (generally) what my function looks like:

exports.myFunctionName = function ( req, res, next )

Document.findOne({ 'document_id' : decodeURIComponent( document_id )}).populate('array_containing_references').exec(function( err, document) 
{
   //Here I need to concatenate all of the embedded arrays, then sort and return the result as JSON (not worried about the sorting).
});

Answer 1

Assuming your input is in the document variable, try this:

var output = document.reduce(function (res, cur) {
  Array.prototype.push.apply(res, cur.array);
  return res;
}, []);

Or this:

var output = [];
document.forEach(function(cur) {
  Array.prototype.push.apply(output, cur.array);
});

Answer 2

You want to take each document and do something with a property from it. Sounds like a great use case for Array.prototype.map !

map will get each document's array value and return you an array of those values. But, you don't want a nested array so we simply use Array.prototype.concat to flatten it. You could also use something like lodash/underscore.js flatten method.

 var a = [ { name: 'test1', array: [1, 2, 3, 4, 5]}, { name: 'test2', array: [1, 2, 3, 4, 5]}, { name: 'test3', array: [1, 2, 3, 4, 5]} ]; var results = Array.prototype.concat.apply([], a.map(function(doc) { return doc.array; })); document.body.innerHTML = results;