pascal_recursive.js

// Print n lines of Pascal's triangle

function new_line(line){
  // function takes the last line and based on that creates the next one
  var new_line_array = [],
      next_int;
  // iterate over the line, which is an array of integers
  for(var i=0; i<line.length; i++ ){
    var a = parseInt(line[i]);
    var b = parseInt(line[i-1]);
    if(isNaN(b)){
      b = 0;
    }
    // next integer is the sum of integers with indexes i and i-1
    next_int = a + b;
    new_line_array.push(next_int);
  }
  new_line_array.push(1);
  // return the new line
  return new_line_array;
}

// here, use the above function recursively, as many times as many lines you want to print
function pascal(n){
  // first line is just '1'
  var last_line = [1];
  // print the initial line, which is line 0
  console.log(last_line.join(' '));
  
  // for as many times as the current iteration no. 
  for(var i=1; i<=n; i++){
    // create next line
    var line = new_line(last_line) ;
    // print the line
    console.log(line.join(' '));
    // assign the new line to last_line
    last_line = line;
  }
}

// print 15 lines of a Pascal's triangle
pascal(15);