Create a hidden text with stereoscopic effect

gen_stereoscopic_hidden_text.ts

var arr = "The old building sighed, each creak a testament to time. Dust motes danced in a lone sunbeam. A layer of grime settled under a neglected wooden bench.  The sharp jangle of a telephone abruptly shattered the pervasive quiet. Near this lonely, forgotten corner, the cold steel doors of the elevator silently waited.".split(' ');
var secret = "under telephone Near elevator".split(' ');
var i = -1;
var MAX_WIDTH = 30;
var lines = [[]];
var _l = 0;

var result = '';

while (i++ < arr.length - 1) {
    if ((_l + arr[i].length) < MAX_WIDTH) {
        if (secret.indexOf(arr[i]) > -1) {arr[i] = (_l?'  ':' ') + arr[i]}
        lines[lines.length - 1].push(arr[i]);
        _l += arr[i].length + 1;

    } else {
        _l = 0;
        i--;
        lines.push([]);
    }
}

for (var i = 0; i < lines.length - 1; putText(lines[i++].join(chars))) {
  // Align text
  var chars = ' ';
  while (lines[i].join(chars + ' ').length < MAX_WIDTH) {
    chars += ' ';
  }
}
putText(lines[i].join(' ') + ' ');
function putText(line) {
  while (line.length < MAX_WIDTH) {
    line = line.replace(' ', '  ');
  }
  // Make the illusion
  result += line;
  for (var val in secret) {
    line = line.split('  '+secret[val]).join(' ' + secret[val] + ' ');
  }
  result += ('   ' + line) + '\n';
}
console.log(result);

output.txt

The  old building sighed, each   The  old building sighed, each
creak     a testament to time.   creak     a testament to time.
Dust    motes danced in a lone   Dust    motes danced in a lone
sunbeam.   A  layer  of  grime   sunbeam.   A  layer  of  grime
settled      under a neglected   settled     under  a neglected
wooden    bench.    The  sharp   wooden    bench.    The  sharp
jangle    of   a     telephone   jangle    of   a    telephone 
abruptly      shattered    the   abruptly      shattered    the
pervasive   quiet.   Near this   pervasive   quiet.  Near  this
lonely,  forgotten corner, the   lonely,  forgotten corner, the
cold     steel  doors  of  the   cold     steel  doors  of  the
    elevator silently waited.       elevator  silently waited.