JavaScript (Node.js) Quick Start Guide for /v1/chat/completions API

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Last updated February 09, 2026

Chat models generate conversational completions for input messages. This guide walks you through how to use the /v1/chat/completions API with JavaScript.

Prerequisites

Before making requests, provision access to the model of your choice.

  1. Attach an inference addon to an app of yours:

    # If you don't have an app yet, you can create one with:
heroku create $APP_NAME # specify the name you want for your app (or skip this step to use an existing app you have)

# Create and attach one of our chat models to your app, $APP_NAME:
heroku addons:create heroku-inference:standard -a $APP_NAME --as INFERENCE

  2. Install the necessary axios package:

    npm install axios

JavaScript Example Code

const axios = require('axios');

// Assert that environment variables are set
const INFERENCE_URL = process.env.INFERENCE_URL;
const INFERENCE_KEY = process.env.INFERENCE_KEY;

if (!INFERENCE_URL || !INFERENCE_KEY) {
    console.error("Missing required environment variables.");
    console.log("Set them up using the following commands:");
    console.log("export INFERENCE_URL=$(heroku config:get -a $APP_NAME INFERENCE_URL)");
    console.log("export INFERENCE_KEY=$(heroku config:get -a $APP_NAME INFERENCE_KEY)");
    process.exit(1);
}

async function parseChatOutput(response) {
    if (response.status === 200) {
        console.log("Chat Completion:", response.data.choices[0].message.content);
    } else {
        console.log(`Request failed: ${response.status}, ${response.statusText}`);
    }
}

async function generateChatCompletion(payload) {
    try {
        const response = await axios.post(`${INFERENCE_URL}/v1/chat/completions`, payload, {
            headers: {
                'Authorization': `Bearer ${INFERENCE_KEY}`,
                'Content-Type': 'application/json'
            }
        });
        await parseChatOutput(response);
    } catch (error) {
        console.error("Error generating chat completion:", error.message);
    }
}

// Example payload
const payload = {
    model: "claude-4-5-sonnet",
    messages: [
        { role: "user", content: "Hello!" },
        { role: "assistant", content: "Hi there! How can I assist you today?" },
        { role: "user", content: "Why is Heroku so cool?" }
    ],
    temperature: 0.5,
    max_tokens: 100,
    stream: false
};

// Generate chat completion
generateChatCompletion(payload);