vuepress/packages/@vuepress/core/lib/util/shared.js

const chalk = require('chalk')

/**
 * Build functional pipeline.
 */
exports.compose = (...processors) => {
  if (processors.length === 0) return input => input
  if (processors.length === 1) return processors[0]
  return processors.reduce((prev, next) => {
    return (...args) => next(prev(...args))
  })
}

exports.isObject = obj => obj !== null && typeof obj === 'object'

/**
 * Get the raw type string of a value e.g. [object Object]
 */
const _toString = Object.prototype.toString

exports.toRawType = value => _toString.call(value).slice(8, -1)

exports.getType = function (fn) {
  const match = fn && fn.toString().match(/^\s*function (\w+)/)
  return match ? match[1] : ''
}

/**
 * Transform multi-types to natural language. e.g.
 *   ['Function']                     => 'Function'
 *   ['Function', 'Object']           => 'Function or Object'
 *   ['Function', 'Object', 'Number'] => 'Function, Object or Number'
 */
function toNaturalMultiTypesLanguage (types) {
  const len = types.length
  if (len === 1) {
    return types.join('')
  }
  const rest = types.slice(0, len - 1)
  const last = types[len - 1]
  return rest.join(', ') + ' or ' + last
}

exports.assertTypes = function (value, types) {
  let valid
  let warnMsg
  let actualType = exports.toRawType(value)
  const expectedTypes = []
  if (actualType === 'AsyncFunction') {
    actualType = 'Function'
  }

  for (const type of types) {
    const expectedType = exports.getType(type)
    expectedTypes.push(expectedType)
    valid = actualType === expectedType
    if (valid) break
  }

  if (!valid) {
    warnMsg =
      `expected a ${chalk.green(toNaturalMultiTypesLanguage(expectedTypes))} ` +
      `but got ${chalk.yellow(actualType)}.`
  }

  return { valid, warnMsg }
}