JS loop through objects

Question

First I am sorry because this possibly will be very simple. But I work a lot in PHP, but that syntax won't work in JS.

I've got the following pieces of code:

var rangeArr = [];
// This piece is inside an loop of adding elements...
rangeArr[row_id] = {"row_x": row_x, "row_y": row_y, "row_name": row_name, "row_dir": row_dir, "row_length": row_length, "row_height": row_height};
 row_id++;

I'll get this object for instance (got from Chrome console):

rangeArr
[undefined ×ばつ 1, 
Object
 row_dir: "lr"
 row_height: "6"
 row_length: "5"
 row_name: ""
 row_x: 45
 row_y: 71
 __proto__: Object
 , 
Object
 row_dir: "lr"
 row_height: "6"
 row_length: "6"
 row_name: ""
 row_x: 95
 row_y: 208
 __proto__: Object
]

I'm using the following piece of code to loop through the object array:

for (var item in rangeArr) {
 if(typeof(item) !== 'undefined'){
 console.log(item.row_x);
 }
}

But I only get undefined errors... When I look into the console log, the whole item contains only the row_id. That means that only the index is retrieved, not the object itself.

As I said before, I have got little to no knowledge about JS Objects, but I thought that this was the right way to do this.

So how can I get my piece of code working so that I can receive the data when needed?

Answer 1

In your for in loop, item is actually the array key, not the array element value. To get the object, use rangeArr[item].

for (var item in rangeArr) {
 var obj = rangeArr[item];
 if(typeof(obj) !== 'undefined'){
 console.log(obj.row_x);
 }
}

That said, for in loops are a bad idea on arrays. A basic incremental for loop, or a forEach is preferred. Refer to this question for more info.

---

It looks like you're generating the incremental keys manually. Instead of that, you might prefer to use Array.prototype.push():

rangeArr.push({"row_x": row_x, "row_y": row_y, "row_name": row_name, "row_dir": row_dir, "row_length": row_length, "row_height": row_height});

• Mathlight: Thank you, that indeed worked. I use the row_id somewhere else to, so the push is not an option. But thank you for your sugestion, didn't knew that was also possible in JS