randomly splice values into array

I have an array "A" of scrambled, randomly generated ASCII characters... and a message "M". I want to insert the characters of message M into array A such that the order of M's characters are intact... but randomly distributed throughout array A.

Original array: zH$@%@$#@$@^^#@(%*$@^&@!$^%&

Sample output: zH$@%@^t$#@$@^^h#@(%*$@^&@i!$^%&s, etc...

                    var randomChars = [];
                    for(var i=33;i<127;++i) {
                        var letter = document.createElement('span');
                        letter.innerHTML = String.fromCharCode(i);
                        randomChars.push(letter);
                    }

                    var message = "this is a message";
                    for (var i = 0; i < message.split("").length; i++) {    
                        var rand = Math.floor((Math.random() * randomChars.length) + 1);
                        var letters = document.createElement('span');
                        letters.innerHTML = message.split("")[i];
                        letters.setAttribute("hidden","");
                        randomChars.splice(rand, 0, letters); 
                    }

Fiddle: http://ift.tt/1DelYzN