code: function stringValue2Buffer(stringValue, byteLength) {
      if ((stringValue).slice(0, 2) === '0x') {
          var input = stringValue.slice(2);
          var length = input.length;
          var buffers = [];
          var j = 0;
          for (var i = length; i > 0 && j < byteLength; i -= 2) {
              buffers.push(new Buffer(input.slice(i - 2, i), 'hex'));
              j++;
          }
          var buffer = Buffer.concat(buffers);
          var paddingLength = byteLength - buffer.length;
          if (paddingLength > 0) {
              var padding = new Buffer(paddingLength);
              padding.fill(0);
              buffer = Buffer.concat([buffer, padding]);
          }
          return buffer;
      }
      else {
          return bigInt2Buffer(new BigInteger(stringValue), byteLength);
      }
  }
docs: Convert a string value to buffer