OpenAI function calling JavaScript example

npm install openai

export OPENAI_API_KEY="your_api_key_here"

import OpenAI from 'openai'

const openai = new OpenAI()

const tools = [
  {
    type: 'function',
    name: 'get_order_status',
    description: 'Get the shipping status for an order ID.',
    parameters: {
      type: 'object',
      properties: {
        orderId: {
          type: 'string',
          description: 'The order ID, for example ORD-1001.',
        },
      },
      required: ['orderId'],
      additionalProperties: false,
    },
    strict: true,
  },
]

function getOrderStatus({ orderId }) {
  const orders = {
    'ORD-1001': 'shipped',
    'ORD-1002': 'processing',
  }

  return {
    orderId,
    status: orders[orderId] || 'not_found',
  }
}

function callFunction(name, args) {
  if (name === 'get_order_status') {
    return getOrderStatus(args)
  }

  throw new Error(`Unknown tool: ${name}`)
}

const input = [
  {
    role: 'user',
    content: 'What is the status of order ORD-1001?',
  },
]

const response = await openai.responses.create({
  model: 'gpt-5.5',
  input,
  tools,
})

for (const item of response.output) {
  if (item.type !== 'function_call') continue

  const args = JSON.parse(item.arguments)
  const result = callFunction(item.name, args)

  input.push(item)
  input.push({
    type: 'function_call_output',
    call_id: item.call_id,
    output: JSON.stringify(result),
  })
}

const finalResponse = await openai.responses.create({
  model: 'gpt-5.5',
  input,
  tools,
})

console.log(finalResponse.output_text)