How to use the @redux-saga/is.string function in @redux-saga/is

export default function matcher(pattern) {
  // prettier-ignore
  const matcherCreator = (
      pattern === '*'            ? wildcard
    : is.string(pattern)         ? string
    : is.array(pattern)          ? array
    : is.stringableFunc(pattern) ? string
    : is.func(pattern)           ? predicate
    : is.symbol(pattern)         ? symbol
    : null
  )

  if (matcherCreator === null) {
    throw new Error(`invalid pattern: ${pattern}`)
  }

  return matcherCreator(pattern)
}

function getFnCallDescriptor(fnDescriptor, args) {
  let context = null
  let fn

  if (is.func(fnDescriptor)) {
    fn = fnDescriptor
  } else {
    if (is.array(fnDescriptor)) {
      ;[context, fn] = fnDescriptor
    } else {
      ;({ context, fn } = fnDescriptor)
    }

    if (context && is.string(fn) && is.func(context[fn])) {
      fn = context[fn]
    }
  }

  return { context, fn, args }
}

let context = null
  let fn

  if (is.array(fnDescriptor)) {
    ;[context, fn] = fnDescriptor
    check(fn, is.notUndef, `${effectName}: argument of type [context, fn] has undefined or null \`fn\``)
  } else if (is.object(fnDescriptor)) {
    ;({ context, fn } = fnDescriptor)
    check(fn, is.notUndef, `${effectName}: argument of type {context, fn} has undefined or null \`fn\``)
  } else {
    check(fnDescriptor, is.func, `${effectName}: argument fn is not function`)
    return
  }

  if (context && is.string(fn)) {
    check(context[fn], is.func, `${effectName}: context arguments has no such method - "${fn}"`)
    return
  }

  check(fn, is.func, `${effectName}: unpacked fn argument (from [context, fn] or {context, fn}) is not a function`)
}