Javascript – Prettify json data in textarea input


I've searched for this particular topic and couldn't find anything similar to it. If there is please close this and give a link.

I'm creating a json data api simulator. I want users to be able to copy and paste a json object request into a textarea where they can also modify it before sending it to the server.

Problem is json obj copy and patses often results in extra spaces and is never aligned properly, even with the pre tag. I also want a good color scheme applied to keys and values.

I've seen plugins, other questions and snippets of code, but they don't apply to textareas where the text is editable. Is there to keep it styled while in edit mode without it showing all the html tags that styled it? I want to be able to write it from scratch with javascript or jquery.

Best Answer

The syntax highlighting is tough but check out this fiddle for pretty printing a json object entered in a text area. Do note that the JSON has to be valid for this to work. (Use the dev console to catch errors.) Check jsLint for valid json.


<textarea id="myTextArea" cols=50 rows=10></textarea>
<button onclick="prettyPrint()">Pretty Print</button>

The js:

function prettyPrint() {
    var ugly = document.getElementById('myTextArea').value;
    var obj = JSON.parse(ugly);
    var pretty = JSON.stringify(obj, undefined, 4);
    document.getElementById('myTextArea').value = pretty;

First try simple input like: {"a":"hello","b":123}

Simple pretty printing of JSON can be done rather easily. Try this js code: (jsFiddle here)

// arbitrary js object:
var myJsObj = {a:'foo', 'b':'bar', c:[false,2,null, 'null']};

// using JSON.stringify pretty print capability:
var str = JSON.stringify(myJsObj, undefined, 4);

// display pretty printed object in text area:
document.getElementById('myTextArea').innerHTML = str;

For this HTML:

<textarea id="myTextArea" cols=50 rows=25></textarea>

And check out JSON.stringify documentation.