Looping through an object and putting result to an array with javascript

Question

I'm trying to loop through an object, to put some values from the object, into a new array. But I have a really hard time figuring out how to do it.

This is my object:

var vehicles = {
    list:{
        "transport":{ //<-- This is the values I want to put to an array
            name:"transport",
            pixelWidth:31,
            pixelHeight:30,
            pixelOffsetX:15,
            pixelOffsetY:15,
            radius:15,
            speed:15,
            sight:3,
            cost:400,
            hitPoints:100,
            turnSpeed:2,
            spriteImages:[
                {name:"stand",count:1,directions:8}         
            ],
        },
        "harvester":{ //<-- This is the values I want to put to an array
            name:"harvester",
            pixelWidth:21,
            pixelHeight:20,
            pixelOffsetX:10,
            pixelOffsetY:10,
            radius:10,
            speed:10,
            sight:3,
            cost:1600,
            hitPoints:50,
            turnSpeed:2,
            spriteImages:[
                {name:"stand",count:1,directions:8}         
            ],
        },
        "scout-tank":{ //<-- This is the values I want to put to an array
            name:"scout-tank",
            canAttack:true,
            canAttackLand:true,
            canAttackAir:false,
            weaponType:"bullet",
            pixelWidth:21,
            pixelHeight:21,
            pixelOffsetX:10,
            pixelOffsetY:10,
            radius:11,
            speed:20,
            sight:3,
            cost:500,
            hitPoints:50,
            turnSpeed:4,
            spriteImages:[
                {name:"stand",count:1,directions:8}         
            ],
        },
        "heavy-tank":{ //<-- This is the values I want to put to an array
            name:"heavy-tank",
            canAttack:true,
            canAttackLand:true,
            canAttackAir:false,
            weaponType:"cannon-ball",
            pixelWidth:30,
            pixelHeight:30,
            pixelOffsetX:15,
            pixelOffsetY:15,
            radius:13,
            speed:15,
            sight:4,
            cost:1200,
            hitPoints:50,
            turnSpeed:4,
            spriteImages:[
                {name:"stand",count:1,directions:8}         
            ],
        }                       
    }

Reading other post, I have the feeling I should use a for-in loop. The real challenge for me, is to get the right value from my object. I've looked at this post to try and solve it.

I come to a solution looking something like this:

var arr = [];

for (var key in vehicles)
    {
        var obj = vehicle[key];
        for (var prop in obj)
            {
                if(obj.hasOwnProperty(prop))
                {
                    arr.push(prop);
                }
            }
    }

console.log(arr);

But I just get this message from console:

Array[0]length: 0__proto__: Array[0]

I also have a running fiddle here

All help would be highly appreciated.

Answer 1

If you just want the ones in vehicles.list:

var arr = Object.keys(vehicles.list);

var vehicles = {
  list:{
    "transport":{ //<-- This is the values I want to put to an array
      name:"transport",
      pixelWidth:31,
      pixelHeight:30,
      pixelOffsetX:15,
      pixelOffsetY:15,
      radius:15,
      speed:15,
      sight:3,
      cost:400,
      hitPoints:100,
      turnSpeed:2,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    },
    "harvester":{ //<-- This is the values I want to put to an array
      name:"harvester",
      pixelWidth:21,
      pixelHeight:20,
      pixelOffsetX:10,
      pixelOffsetY:10,
      radius:10,
      speed:10,
      sight:3,
      cost:1600,
      hitPoints:50,
      turnSpeed:2,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    },
    "scout-tank":{ //<-- This is the values I want to put to an array
      name:"scout-tank",
      canAttack:true,
      canAttackLand:true,
      canAttackAir:false,
      weaponType:"bullet",
      pixelWidth:21,
      pixelHeight:21,
      pixelOffsetX:10,
      pixelOffsetY:10,
      radius:11,
      speed:20,
      sight:3,
      cost:500,
      hitPoints:50,
      turnSpeed:4,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    },
    "heavy-tank":{ //<-- This is the values I want to put to an array
      name:"heavy-tank",
      canAttack:true,
      canAttackLand:true,
      canAttackAir:false,
      weaponType:"cannon-ball",
      pixelWidth:30,
      pixelHeight:30,
      pixelOffsetX:15,
      pixelOffsetY:15,
      radius:13,
      speed:15,
      sight:4,
      cost:1200,
      hitPoints:50,
      turnSpeed:4,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    }    
  }
};
var arr = Object.keys(vehicles.list);
snippet.log(arr.join(", "));

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<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

If you want all of the keys of the objects referenced by any property of vehicles, then:

var arr = [];
Object.keys(vehicles).forEach(function(key) {
  arr.push.apply(arr, Object.keys(vehicles[key]));
});

The trick there is that we can push an entire array of entries onto arr using arr.push.apply(arr, /*the other array*/).

var vehicles = {
  list:{
    "transport":{ //<-- This is the values I want to put to an array
      name:"transport",
      pixelWidth:31,
      pixelHeight:30,
      pixelOffsetX:15,
      pixelOffsetY:15,
      radius:15,
      speed:15,
      sight:3,
      cost:400,
      hitPoints:100,
      turnSpeed:2,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    },
    "harvester":{ //<-- This is the values I want to put to an array
      name:"harvester",
      pixelWidth:21,
      pixelHeight:20,
      pixelOffsetX:10,
      pixelOffsetY:10,
      radius:10,
      speed:10,
      sight:3,
      cost:1600,
      hitPoints:50,
      turnSpeed:2,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    },
    "scout-tank":{ //<-- This is the values I want to put to an array
      name:"scout-tank",
      canAttack:true,
      canAttackLand:true,
      canAttackAir:false,
      weaponType:"bullet",
      pixelWidth:21,
      pixelHeight:21,
      pixelOffsetX:10,
      pixelOffsetY:10,
      radius:11,
      speed:20,
      sight:3,
      cost:500,
      hitPoints:50,
      turnSpeed:4,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    },
    "heavy-tank":{ //<-- This is the values I want to put to an array
      name:"heavy-tank",
      canAttack:true,
      canAttackLand:true,
      canAttackAir:false,
      weaponType:"cannon-ball",
      pixelWidth:30,
      pixelHeight:30,
      pixelOffsetX:15,
      pixelOffsetY:15,
      radius:13,
      speed:15,
      sight:4,
      cost:1200,
      hitPoints:50,
      turnSpeed:4,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    }    
  },
  list2: {
    "new-key-for-list2":{
      }
  }
};
var arr = [];
Object.keys(vehicles).forEach(function(key) {
  arr.push.apply(arr, Object.keys(vehicles[key]));
});
snippet.log(arr.join(", "));

<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

Or if you really like one-liners, you could use Array#reduce but I think clarity suffers:

var arr = Object.keys(vehicles).reduce(function(a, key) {
  a.push.apply(a, Object.keys(vehicles[key]));
  return a;
}, []);

var vehicles = {
  list:{
    "transport":{ //<-- This is the values I want to put to an array
      name:"transport",
      pixelWidth:31,
      pixelHeight:30,
      pixelOffsetX:15,
      pixelOffsetY:15,
      radius:15,
      speed:15,
      sight:3,
      cost:400,
      hitPoints:100,
      turnSpeed:2,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    },
    "harvester":{ //<-- This is the values I want to put to an array
      name:"harvester",
      pixelWidth:21,
      pixelHeight:20,
      pixelOffsetX:10,
      pixelOffsetY:10,
      radius:10,
      speed:10,
      sight:3,
      cost:1600,
      hitPoints:50,
      turnSpeed:2,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    },
    "scout-tank":{ //<-- This is the values I want to put to an array
      name:"scout-tank",
      canAttack:true,
      canAttackLand:true,
      canAttackAir:false,
      weaponType:"bullet",
      pixelWidth:21,
      pixelHeight:21,
      pixelOffsetX:10,
      pixelOffsetY:10,
      radius:11,
      speed:20,
      sight:3,
      cost:500,
      hitPoints:50,
      turnSpeed:4,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    },
    "heavy-tank":{ //<-- This is the values I want to put to an array
      name:"heavy-tank",
      canAttack:true,
      canAttackLand:true,
      canAttackAir:false,
      weaponType:"cannon-ball",
      pixelWidth:30,
      pixelHeight:30,
      pixelOffsetX:15,
      pixelOffsetY:15,
      radius:13,
      speed:15,
      sight:4,
      cost:1200,
      hitPoints:50,
      turnSpeed:4,
      spriteImages:[
        {name:"stand",count:1,directions:8}         
      ],
    }    
  },
  list2: {
    "new-key-for-list2":{
      }
  }
};
var arr = Object.keys(vehicles).reduce(function(a, key) {
  a.push.apply(a, Object.keys(vehicles[key]));
  return a;
}, []);
snippet.log(arr.join(", "));

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<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

---

Note that Object.keys and Array#forEach (and Array#reduce) were all added in ES5 (2009-ish), so they're in all modern browsers, but missing from IE8 and other similar old browsers. All three can be polyfilled, though.

Answer 2

When iterating with a for in loop you get the key in each iteration. This key should be used to access the value from the original array. In your loop you are accessing a non existing(as far as I can see) variable - vehicle. Change it to the array's name - vehicles:

var arr = [];

for (var key in vehicles)
    {
        var obj = vehicles[key];
        for (var prop in obj)
            {
                if(obj.hasOwnProperty(prop))
                {
                    arr.push(prop);
                }
            }
    }

console.log(arr);