[Javascript] Create an Array concatAll method

In addition to flat Arrays, programmers must often deal with nested Arrays. For example let's say we have an Array of stock exchanges, each of which is represented by an array of all the stocks listed on that exchange. If we were looking for a stock that matched a certain criteria, we would first need to loop through all of the exchanges, and then all of the stocks within.

In these situations, most developers would nest two loops. However in this lesson we will write a new Array function "concatAll" which will automatically flatten nested arrays buy one dimension. This will remove the need to ever use a nested loop to flatten a nested array.

 

var exchanges = [
  [
      { symbol: "XFX", price: 240.22, volume: 23432 },
      { symbol: "TNZ", price: 332.19, volume: 234 }
    ],
  [
      { symbol: "JXJ", price: 120.22, volume: 5323 },
      { symbol: "NYN", price: 88.47, volume: 98275 }
    ]
];


Array.prototype.concatAll = function() {
  var results = [];
  
  this.forEach(function(subArray) {
    subArray.forEach(function(item) {
      results.push(item);    
    });
  });  

  return results;
};


var stocks =  exchanges.concatAll();
    
stocks.forEach(function(stock) {       
  console.log(JSON.stringify(stock));  
});

 

Also see lodash flatten: 

_.flatten(array, [isDeep])

https://lodash.com/docs#flatten