How do I loop through a JavaScript object?

Question

I'm trying to loop through this object and modify some values however I'm getting just the key when I log it.

this.restProviderService.getMessages(this.gameService.getStepId(), this.gameService.teamId).subscribe(messages => { console.log(messages); for (var m in messages) { console.log(m); } });

console.log(messages)

[ { "id": "3", "chatId": "1_1", "user_id": "21", "userName": "batman", "msg": "banananananana", "createdAt": "1632507755" }, { "id": "2", "chatId": "1_1", "user_id": "31", "userName": "jennyg", "msg": "asdfasdfasdf", "createdAt": "1632507721" } ]

Console.log(m)

0 1

when I use "of" I get Type 'Messages' is not an array type or a string type. — user2570937
– user2570937, Commented Sep 25, 2021 at 0:37

Gareth · Accepted Answer · 2021-09-25 00:29:16Z

1

A for in loop in JS gives you the key. What you do is

 for (var m in messages) { var message = messages[m]; console.log(message); }

or

 for (var m of messages) { console.log(m); }

answered Sep 25, 2021 at 0:29

Gareth

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3 Comments

user2570937 Over a year ago

When I use of I get "Type 'Messages' is not an array type or a string type."

Gareth Over a year ago

What does console.log(typeof messages) give you? If it's an object the first option should still work.

user2570937 Over a year ago

yes the first one works. just wondering why the 2nd one doesnt

kelortondo · Accepted Answer · 2021-09-25 00:47:04Z

You are looking for a for...of loop.

In Javascript, a for...in loop will return the index each iteration. (0, 1, so on)

A for...of loop will return the item at each sequential index.

 for (var m of messages) { console.log(m); //Will log each item in the array in order }

You could also use the array method forEach:

messages.forEach((m, index) => { console.log(m); // Will print each object console.log(index); // 0, 1, 2 });

Relevant MDN

You may also be having trouble because you are dealing with an "array-like object", which can be returned from some methods. Here are some ways to convert it to a usual array. But, TLDR:

 let typicalArray = [...messages]; //Do stuff with typicalArray

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