How to parse JSON to object with lower case key

That is function:

function JSON_Lower_keys(J) {
   var ret={};
   $.map(JSON.parse(J),function(value,key){
             ret[key.toLowerCase()]=value;
   })
   return ret;
}

that is call:

console.log(JSON_Lower_keys('{"ID":1234, "CONTENT":"HELLO"}'))

How about this:

json.replace(/"([^"]+)":/g,function($0,$1){return ('"'+$1.toLowerCase()+'":');}));

The regex captures the key name $1 and converts it to lower case.

Live demo: http://jsfiddle.net/bHz7x/1/

[edit] To address @FabrícioMatté's comment, another demo that only matches word characters: http://jsfiddle.net/bHz7x/4/

Iterate over the properties and create lowercase properties while deleting old upper case ones:

var str = '{"ID":1234, "CONTENT":"HELLO"}';

var obj = $.parseJSON(str);
$.each(obj, function(i, v) {
    obj[i.toLowerCase()] = v;
    delete obj[i];
});

console.log(obj);
//{id: 1234, content: "HELLO"} 

Fiddle

Or you can just build a new object from the old one's properties:

var obj = $.parseJSON(str),
    lowerCased = {};
$.each(obj, function(i, v) {
    lowerCased[i.toLowerCase()] = v;
});

Fiddle

References:

• jQuery.each
• String.toLowerCase