Support `decimal.js`

[kth-tw]

I try to compare two Decimal (use decimal.js package)

chai.assert.containSubset({ a: new Decimal(123) }, { a: new Decimal(123) })

And got error

     Error: [DecimalError] Invalid argument: function Decimal(v) {
      var e, i, t,
        x = this;

      // Decimal called without new.
      if (!(x instanceof Decimal)) return new Decimal(v);

      // Retain a reference to this Decimal constructor, and shadow Decimal.prototype.constructor
      // which points to Object.
      x.constructor = Decimal;

      // Duplicate.
      if (isDecimalInstance(v)) {
        x.s = v.s;

        if (external) {
          if (!v.d || v.e > Decimal.maxE) {

            // Infinity.
            x.e = NaN;
            x.d = null;
          } else if (v.e < Decimal.minE) {

            // Zero.
            x.e = 0;
            x.d = [0];
          } else {
            x.e = v.e;
            x.d = v.d.slice();
          }
        } else {
          x.e = v.e;
          x.d = v.d ? v.d.slice() : v.d;
        }

        return;
      }

      t = typeof v;

      if (t === 'number') {
        if (v === 0) {
          x.s = 1 / v < 0 ? -1 : 1;
          x.e = 0;
          x.d = [0];
          return;
        }

        if (v < 0) {
          v = -v;
          x.s = -1;
        } else {
          x.s = 1;
        }

        // Fast path for small integers.
        if (v === ~~v && v < 1e7) {
          for (e = 0, i = v; i >= 10; i /= 10) e++;

          if (external) {
            if (e > Decimal.maxE) {
              x.e = NaN;
              x.d = null;
            } else if (e < Decimal.minE) {
              x.e = 0;
              x.d = [0];
            } else {
              x.e = e;
              x.d = [v];
            }
          } else {
            x.e = e;
            x.d = [v];
          }

          return;

        // Infinity, NaN.
        } else if (v * 0 !== 0) {
          if (!v) x.s = NaN;
          x.e = NaN;
          x.d = null;
          return;
        }

        return parseDecimal(x, v.toString());

      } else if (t !== 'string') {
        throw Error(invalidArgument + v);
      }

      // Minus sign?
      if ((i = v.charCodeAt(0)) === 45) {
        v = v.slice(1);
        x.s = -1;
      } else {
        // Plus sign?
        if (i === 43) v = v.slice(1);
        x.s = 1;
      }

      return isDecimal.test(v) ? parseDecimal(x, v) : parseOther(x, v);
    }

Could you support decimal.js ?