Question

I need the following two codes
1) A code to select all variables that begin with “example”
2) A code to select all variables that have “true” as value for “available”

example1= {price:1000, size: 1000, available:true}
example2= {price:2000, size: 2000, available:false}
example3= {price:3000, size: 3000, available:true}
example4= {price:4000, size: 4000, available=true}

This is what I want to achieve with code one. As there are a lot of variables I need a quick way of doing it:

var allexampleprices=[example1.price, example2.price, example3.price, example4.price]

With the second code I want to get an array with all the names of the variables that contain the value “false”

Any help appreciated!

Answer 1

All of these are the exact same thing, assuming you’re not in a function:

var myVar       = 7;
window.myVar    = 7;
window["myVar"] = 7;

Therefore, you can access any global variable (a variable defined outside a function) by using the window[ insertString ] method. If you wanted to search through every property on the window object to find one called example, you’d do:

for( var k in window ){
  if(/example/.test(k)){
    var myExample = window[k];
    // Do stuff
  }
}

I would HIGHLY recommend against this method, though, for many reasons. To start, it’s a horribly bad practice to put anything in the global scope. Variables will start colliding all over the place on big projects. Also, the window object has soooooo many properties that searching through all of them is a horrible performance drain.

Having said all of that, I’ve devised an example of what you should do, including the helper functions to do it:

var objects =
{
  example1:
  {
    price: 1000,
    size: 1000,
    available: true
  },

  example2:
  {
    price: 2000,
    size: 2000,
    available: false
  },

  example3:
  {
    price: 3000,
    size: 3000,
    available: true
  },

  example4:
  {
    price: 4000,
    size: 4000,
    available: true
  }
}

function filter(obj, comparator){
  var list = [];
  for(var k in obj){
    if(obj.hasOwnProperty(k)){ // fix for IE
      if(comparator(obj[k], k, obj)) list.push(obj[k]);
    }
  }
  return list;
}

function isExample(obj, key){
  if(/^example/.test( key.toLowerCase() )) return true;
}

function isAvailable(obj){
  if(obj.available) return true;
}

/**
 * And here's how you use it
 */

var examples  = filter(objects, isExample);
var available = filter(objects, isAvailable);

var availableExample = filter(examples, isAvailable);

The filter function returns an array of all of the matching objects.

— EDIT —

You want it to say the names of the objects in the console. I’m assuming what you mean is that the console currently shows [object, object, object, object]. There are two ways to do this:

(1) Put the name in the object itself

example1:
{
  name: "example1",
  price: 1000,
  size: 1000,
  available: true
}

(2) Capture the name in the filter operation

var names = [];
var examples  = filter(objects, function(obj, name){
  if(/^example/.test( name.toLowerCase() )){
    names.push(name);
    return true;
  }
});

console.log(names);