Create JSON string from javascript for loop

Question

I want to create a JSON string from a javascript for loop. This is what I tried to do (which gives me something that looks like a JSON string), but it does not work.

var edited = "";
for(var i=1;i<POST.length-1;i++) {
    edited += '"'+POST[i].name+'":"'+POST[i].value+'",';
}

It gives me this:

"type":"empty","name":"email-address","realname":"Email Address","status":"empty","min":"empty","max":"empty","dependson":"empty",

This does not work if I try to convert it into a JSON object later.

This was my expected result: {"type":"empty","name":"empty","realname":"empty","status":"empty","min":"empty","max":"empty","dependson":"empty","matches":"empty"}. Problem solved — Sthe
– Sthe, Commented Aug 8, 2011 at 8:45

Digital Plane · Accepted Answer · 2011-08-08 08:02:26Z

Two problems:

You want an object, so the JSON string has to start with { and end with }.
There is a trailing , which may be recognized as invalid.

It's probably better to use a library, but to correct your code:

Change var edited = ""; to var edited = "{"; to start your JSON string with a {
Add edited = edited.slice(0, -1); after the for loop to remove the trailing comma.
Add edited += "}"; after the previous statement to end your JSON string with a }

Your final code would be:

var edited = "{";
for(var i=1;i<POST.length-1;i++) {
    edited += '"'+POST[i].name+'":"'+POST[i].value+'",';
}
edited = edited.slice(0, -1);
edited += "}";

Again, it's best to use a library (e.g. JSON.stringify) by making an object with a for loop, adding properties by using POST[i].name as a key and POST[i].value as the value, then using the library to convert the object to JSON.

Also, you are starting with index 1 and ending with index POST.length-2, therefore excluding indices 0 (the first value) and POST.length-1 (the last value). Is that what you really want?

Praveen Prasad · Accepted Answer · 2011-08-08 08:11:51Z

4

//dummy data
var post=[{name:'name1',value:1},{name:'name2',value:2}];

var json=[];
for(var i=0;i<post.length;i++)
{
    var temp={};
    temp[post[i].name]=post[i].value;
   json.push(temp);
}

var stringJson = JSON.stringify(json);


alert(stringJson );

http://jsfiddle.net/3mYux/

edited Aug 8, 2011 at 8:11

answered Aug 8, 2011 at 7:52

Praveen Prasad

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1 Comment

Sthe Over a year ago

Thank you. Im getting an error at json.push({POST[i].name:POST[i].value});. It say Unexpected Identifier.

Im0rtality · Accepted Answer · 2011-08-08 07:50:27Z

0

You have extra comma in your JSON string. JSON string format: {"JSON": "Hello, World"}

var edited = "{";
for(var i=1;i<POST.length-1;i++) {
    edited += '"'+POST[i].name+'":"'+POST[i].value+'",';
}
// remove last comma:
edited = edited.substring(0, edited.length-1) + "}";

answered Aug 8, 2011 at 7:50

Im0rtality

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Comments

Tomas Jansson · Accepted Answer · 2011-08-08 07:54:54Z

0

Can't you just build up a hash and do toString on the hash? Something like this:

var edited = {};
for(var i=0;i<POST.length-1;i++) {    
    edited[POST[i].name] = POST[i].value;
}

Or maybe JSON.stringify is what you are looking for: http://www.json.org/js.html

edited Aug 8, 2011 at 7:54

answered Aug 8, 2011 at 7:49

Tomas Jansson

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