calcString() {
    let actions = [
      this.tryCalcOperation,
      this.isOperation ? this.tryCalcPercent : null,
      this.tryCalcVar,
      this.tryCalcRem,
    ].filter(Boolean);
    let value = this.tryActions(actions, this.value);
    if (value !== null) {
      this.outValue = value;
    } else {
      this.proxyValue();
    }
  }
Calculates string
Here we do not calc direct percent values as they supported natively since RN 43 (#32).
But keep calculating percent for operands when value defined as operation.