Use:
var queryStringParts = queryString.split('&');
var pairs = queryStringParts.map(function(str) { return str.split('=') })
var rewrittenParts = pairs.map(function(pair){
return 'slides[0].' + pair[0] + '=' + pair[1]
});
var newQuerystring = rewrittenParts.join('&');
As was pointed out in the comments, in this specific case we could skip the split into pairs step and just do
var queryStringParts = queryString.split('&');
var rewrittenParts = queryStringParts.map(function(part) {
return 'slides[0].' + part
});
var newQuerystring = rewrittenParts.join('&');
6
solved In JavaScript, what is the simplest way to insert text into a string?