triangle_recursive_printing.js

/**
 * @message {String}
 */

function myFunction(message) {
  
  // Need the index counter which I'll mention
  // the reason on below comment
  var printString = function(str, i) {
    if(i === 0) return;
    
    i = i || 1;
    
    /**
     * Checkpoint where function is printing all the words.
     * In this case, if user pass in 'abc' then this checkpoint
     * is checking if function already printing whole 'abc'
     * 
     * If so then return by calling self function 
     * with new negative index so the printing will be in reverse
     */
    if(i > str.length) return printString(str, -1 * str.length + 1);
    
    // Math.abs is required to convert negative number to positive
    console.log(str.substr(0, Math.abs(i)));
    return printString(str, i+1) ;
  }

  if (!message || message && typeof message != 'string') return;
  
  return printString(message);
}

/**
* It will print :
*
* a
* ab
* abc
* ab
* a
*/

myFunction('abc');