How to use the jstat.jStat.gamma function in jstat

private generateIdentifier(): string {
    const length = Math.ceil(jStat.gamma.sample(ID_GAMMA_SHAPE, ID_GAMMA_SCALE)) as number;
    let identifier = ALPHA_CHARSET[Math.floor(Math.random() * ALPHA_CHARSET.length)];

    for (let i = 1; i < length; i += 1) {
      identifier += ALPHA_NUMERIC_CHARSET[Math.floor(Math.random() * ALPHA_NUMERIC_CHARSET.length)];
    }

    if (keywords.has(identifier.toLowerCase())) {
      return this.generateIdentifier();
    }
    return identifier;
  }

var Finance = require('financejs')
const finance = new Finance()

const jStatDistributions = {
  beta: jStat.beta.sample,
  centralF: jStat.centralF.sample,
  cauchy: jStat.cauchy.sample,
  chisquare: jStat.chisquare.sample,
  exponential: jStat.exponential.sample,
  invgamma: jStat.invgamma.sample,
  lognormal: jStat.lognormal.sample,
  normal: jStat.normal.sample,
  studentt: jStat.studentt.sample,
  weibull: jStat.weibull.sample,
  uniform: jStat.uniform.sample,
  gamma: jStat.gamma.sample
}

const financeFunctions = {
  PV: finance.PV,
  FV: finance.FV,
  NPV: finance.NPV,
  //IRR: finance.IRR, Too slow.
  PP: finance.PP,
  ROI: finance.ROI,
  AM: finance.AM,
  PI: finance.PI,
  DF: finance.DF,
  CI: finance.CI,
  CAGR: finance.CAGR,
  LR: finance.LR,
  R72: finance.R72,

return min + p*width
}

export const Distributions = {
  beta: jStat.beta.sample,
  centralF: jStat.centralF.sample,
  cauchy: jStat.cauchy.sample,
  chisquare: jStat.chisquare.sample,
  exponential: jStat.exponential.sample,
  invgamma: jStat.invgamma.sample,
  lognormal: jStat.lognormal.sample,
  normal: jStat.normal.sample,
  studentt: jStat.studentt.sample,
  weibull: jStat.weibull.sample,
  uniform: jStat.uniform.sample,
  gamma: jStat.gamma.sample,
  triangular,
  doubleTriangular,
  PERT,
  bernoulli: bernoulli,
  if: bernoulli,
  test: bernoulli,
  binomial: binomial,
  poisson: poisson,
  negBinomial: negBinomial
}

private generateString(): string {
    const length = jStat.gamma.sample(STRING_GAMMA_SHAPE, STRING_GAMMA_SCALE) as number;
    return `"${this.generateRandomString(length)}"`;
  }