interval notationをパースするJavaScript

IntervalNotation.js

// Usage: new IntervalNotation('[−3,1]').test(1) => true
// What's interval notation? see: https://www.varsitytutors.com/hotmath/hotmath_help/topics/interval-notation
class IntervalNotation {
  constructor(str) {
    const [left, right] = str.split(',')

    if (!right) {
      if (left.startsWith('[') || left.startsWith('(')) {
        // Upper limit is omitted
        this._lowwerCond = getLowwerCond(left)
        this._upperCond = (_) => true
      }

      if (left.endsWith(']') || left.endsWith(')')) {
        // Lowwer limit is omitted
        this._lowwerCond = (_) => true
        this._upperCond = getUpperCond(left)
      }
    } else {
      this._lowwerCond = getLowwerCond(left)
      this._upperCond = getUpperCond(right)
    }

    if (!this._lowwerCond || !this._upperCond) {
      throw `${str} is not valid interval notation`
    }
  }

  test(value) {
    return this._lowwerCond(value) && this._upperCond(value)
  }
}

function getLowwerCond(str) {
  if (str.startsWith('[')) {
    return (right) => gte(parseFloat(str.replace('[', '')), right)
  }
  if (str.startsWith('(')) {
    return (right) => gt(new Number(str.replace('(', '')), right)
  }
  throw `${str} is not valid interval notation`
}

function getUpperCond(str) {
  if (str.endsWith(']')) {
    return (left) => gte(left, new Number(str.replace(']', '')))
  }
  if (str.endsWith(')')) {
    return (left) => gt(left, new Number(str.replace(')', '')))
  }
  throw `${str} is not valid interval notation`
}

function gt(left, right) {
  return left < right
}

function gte(left, right) {
  return left <= right
}