var numbers = [1,2,3,4,5,6,7,8,9];
var target = 100;

function getPaddedBase3String(number, padding) {
  return ("0".repeat(padding) + number.toString(3).split()).slice(-padding);
}

function getSumText(signs) {
  var sumText = numbers[0].toString();
  for (var i = 0; i < numbers.length-1; i++) {
    if (signs[i] == '1') {
      sumText += '+';
    }
    else if (signs[i] == '2') {
      sumText += '-';
    }
    sumText += numbers[i+1].toString();
  }
  return sumText;
}


var possibilities = Math.pow(3, numbers.length-1);
for (var i = 0; i < possibilities; i++) {
  var sumText = getSumText(getPaddedBase3String(i, numbers.length-1).split(''));
  var sum = eval(sumText);
  if (sum === target) {
    console.log(sumText, ' = ', target);
  }
}