form-data-body/index.js

A tiny, dependency-free node module for generating a form's multipart/form-data body for a POST request.

'use strict'

module.exports = (fields, boundary) => {
  let body = ''

  if (!boundary) {
    boundary = module.exports.generateBoundary()
  } else if (typeof boundary !== 'string') {
    throw new TypeError('`boundary` parameter should be a string.')
  }

  if (fields && fields.constructor === Object) {
    for (let fieldName in fields) {
      let fieldData = fields[fieldName]

      if (Array.isArray(fieldData)) {
        fieldName += '[]'
      } else {
        fieldData = [fieldData]
      }

      if (!fieldData.length) {
        fieldData = [null]
      }

      fieldData.forEach(field => {
        if (field && field.constructor === Object) {
          if (!field.name || typeof field.name !== 'string') {
            throw new TypeError(`\`fields.${fieldName}.name\` should be a string.`)
          } else if (!field.type || typeof field.type !== 'string') {
            throw new TypeError(`\`fields.${fieldName}.type\` should be a string.`)
          } else if (!field.data || typeof field.data !== 'string') {
            throw new TypeError(`\`fields.${fieldName}.data\` should be a string.`)
          } else {
            body += `--${boundary}\r\n`
            body += `Content-Disposition: form-data; name="${fieldName}"; filename="${field.name}"\r\n`
            body += `Content-Type: ${field.type}\r\n\r\n`
            body += `${field.data}\r\n`
          }
        } else if (typeof field === 'string') {
          body += `--${boundary}\r\n`
          body += `Content-Disposition: form-data; name="${fieldName}"\r\n\r\n`
          body += `${field}\r\n`
        } else {
          throw new TypeError(`\`fields.${fieldName}\` is an unsupported type, should be an object, string, or an array that contains those two types.`)
        }
      })
    }

    if (body.length) {
      body += `--${boundary}--\r\n`
    }
  } else {
    throw new TypeError('`fields` parameter is required and should be an object.')
  }

  return body
}

module.exports.generateBoundary = () => {
  let boundary = '--------------------------'

  for (let i = 0; i < 24; i++) {
    boundary += Math.floor(Math.random() * 10).toString(16)
  }

  return boundary
}