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<!DOCTYPE html>
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  <meta charset="UTF-8">
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  <title>JavaScript SDK - Local Web Services</title>
  <meta name="description" content="local-web-services-javascript-sdk: Jest AWS service testing for Node.js. Pre-configured AWS SDK v3 clients and automatic endpoint redirection via environment variables.">
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  <nav class="nav">
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      <a href="index.html" class="nav-logo">Local Web Services</a>
      <ul class="nav-links">
        <li><a href="getting-started.html">Get Started</a></li>
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  </nav>

  <header class="page-header">
    <div class="container">
      <h1>JavaScript SDK</h1>
      <p class="section-lead">AWS service testing for Node.js. When a session starts, <code>AWS_ENDPOINT_URL_*</code> environment variables are set automatically — every AWS SDK v3 client in your application talks to local services without any code changes.</p>
      <div style="display: flex; gap: 16px; justify-content: center; margin-top: 24px; flex-wrap: wrap;">
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        <a href="https://github.com/local-web-services/local-web-services/tree/main/lang/javascript/example" class="btn btn-secondary">Example Project</a>
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      </div>
    </div>
  </header>

  <!-- Quick Start -->
  <section class="section">
    <div class="container">
      <h2>Quick Start</h2>
      <p class="section-lead">Install, create a session in <code>beforeAll</code>, and write a test. Local services start as a subprocess — your application's AWS SDK clients redirect to them automatically.</p>

      <div class="steps" style="max-width: 900px;">
        <div class="step">
          <div class="step-number">1</div>
          <div class="step-content">
            <h3>Install</h3>
            <div class="code-block">
              <code>npm install local-web-services-javascript-sdk
# also requires local-web-services (Python) for ldk dev
pip install local-web-services</code>
            </div>
          </div>
        </div>
        <div class="step">
          <div class="step-number">2</div>
          <div class="step-content">
            <h3>Configure Jest</h3>
            <div class="code-block">
              <code>// jest.config.js
module.exports = {
  testEnvironment: 'node',
  testTimeout: 60000,  // allow time for ldk dev to start
};</code>
            </div>
          </div>
        </div>
        <div class="step">
          <div class="step-number">3</div>
          <div class="step-content">
            <h3>Write your test</h3>
            <div class="code-block">
              <code>// orders.test.js
const { LwsSession } = require('local-web-services-javascript-sdk');

let session;

beforeAll(async () => {
  session = await LwsSession.create({
    tables: [{ name: 'Orders', partitionKey: 'id' }],
    queues: ['OrderQueue'],
  });
});

afterAll(async () => {
  await session.close();
});

beforeEach(async () => {
  await session.reset();  // wipe state between tests
});

test('creates an order', async () => {
  // Call your real application code — it uses standard AWS SDK clients
  const { createOrder } = require('./orders');
  await createOrder({ id: '42', status: 'pending' });

  // Assert using the DynamoDB helper
  const table = session.dynamodb('Orders');
  const item = await table.assertItemExists({ id: { S: '42' } });
  expect(item.status.S).toBe('pending');
});

test('order sends a queue message', async () => {
  const { createOrder } = require('./orders');
  await createOrder({ id: '99', status: 'pending' });

  const queue = session.sqs('OrderQueue');
  await queue.assertMessageCount(1);
});</code>
            </div>
          </div>
        </div>
        <div class="step">
          <div class="step-number">4</div>
          <div class="step-content">
            <h3>Run your tests</h3>
            <div class="code-block">
              <code>npx jest</code>
            </div>
            <p style="margin-top: 12px; color: var(--color-text-muted);">The session starts <code>ldk dev</code> once in <code>beforeAll</code>, then <code>reset()</code> wipes state before each test.</p>
          </div>
        </div>
      </div>
    </div>
  </section>

  <!-- Drop-in replacement -->
  <section class="section section-alt">
    <div class="container">
      <h2>Drop-in Replacement — Zero Code Changes</h2>
      <p class="section-lead">When a session starts, <code>AWS_ENDPOINT_URL_*</code> environment variables are set for every supported service. Any <code>new DynamoDBClient({})</code> your application creates will automatically use local services — no client reconfiguration, no dependency injection.</p>

      <div class="comparison comparison--code">
        <div class="comparison-col">
          <h3>Your application code</h3>
          <div class="code-block" style="margin-top: 16px;">
            <code>// orders.js  — unchanged
const { DynamoDBClient, PutItemCommand } = require('@aws-sdk/client-dynamodb');
const { SQSClient, SendMessageCommand } = require('@aws-sdk/client-sqs');

// Standard clients — no endpoint config
const dynamo = new DynamoDBClient({});
const sqs    = new SQSClient({});

async function createOrder(order) {
  await dynamo.send(new PutItemCommand({
    TableName: 'Orders',
    Item: {
      id:     { S: order.id },
      status: { S: order.status },
    },
  }));

  await sqs.send(new SendMessageCommand({
    QueueUrl:    process.env.ORDER_QUEUE_URL,
    MessageBody: JSON.stringify(order),
  }));
}

module.exports = { createOrder };</code>
          </div>
        </div>
        <div class="comparison-col">
          <h3>Your test</h3>
          <div class="code-block" style="margin-top: 16px;">
            <code>// orders.test.js
const { LwsSession } = require('local-web-services-javascript-sdk');

let session;

beforeAll(async () => {
  session = await LwsSession.create({
    tables: [{ name: 'Orders', partitionKey: 'id' }],
    queues: ['OrderQueue'],
  });
  // AWS_ENDPOINT_URL_DYNAMODB and AWS_ENDPOINT_URL_SQS
  // are now set — the clients in orders.js pick them
  // up automatically on their next call.
});

test('creates an order', async () => {
  const { createOrder } = require('./orders');
  await createOrder({ id: '42', status: 'pending' });

  await session.dynamodb('Orders')
    .assertItemExists({ id: { S: '42' } });

  await session.sqs('OrderQueue')
    .assertMessageCount(1);
});</code>
          </div>
        </div>
      </div>

      <div class="feature-grid" style="margin-top: 48px;">
        <div class="feature-card">
          <div class="feature-icon">&#127757;</div>
          <h3>Env Var Injection</h3>
          <p>Sets <code>AWS_ENDPOINT_URL_DYNAMODB</code>, <code>AWS_ENDPOINT_URL_SQS</code>, <code>AWS_ENDPOINT_URL_S3</code>, and more. Restored to original values when <code>session.close()</code> is called.</p>
        </div>
        <div class="feature-card">
          <div class="feature-icon">&empty;</div>
          <h3>No Refactoring</h3>
          <p>Application code is identical to production. <code>new DynamoDBClient({})</code> without any endpoint override just works — the AWS SDK v3 reads the env var automatically.</p>
        </div>
        <div class="feature-card">
          <div class="feature-icon">&#128275;</div>
          <h3>No Credentials</h3>
          <p>Local services accept any credentials. No AWS account, no IAM setup, no <code>~/.aws/credentials</code> needed in your test environment.</p>
        </div>
      </div>
    </div>
  </section>

  <!-- LwsSession API -->
  <section class="section">
    <div class="container">
      <h2>LwsSession</h2>
      <p class="section-lead">All factory methods are async — they start <code>ldk dev</code> and wait until services are ready before resolving.</p>

      <h3 class="section-subheading section-subheading--primary">Factory methods</h3>
      <div class="code-block config-example">
        <code>const { LwsSession } = require('local-web-services-javascript-sdk');

// Explicit resource declaration
const session = await LwsSession.create({
  tables: [
    { name: 'Orders', partitionKey: 'id' },
    { name: 'Products', partitionKey: 'sku', sortKey: 'version' },
  ],
  queues: ['OrderQueue', 'DeadLetterQueue'],
  buckets: ['ReceiptsBucket'],
});

// Auto-discover from CDK cloud assembly (cdk.out/)
const session = await LwsSession.fromCdk('../my-cdk-project');

// Auto-discover from Terraform .tf files
const session = await LwsSession.fromHcl('../my-terraform-project');

// Always close after your tests
await session.close();</code>
      </div>

      <h3 class="section-subheading section-subheading--primary">Client factory and utilities</h3>
      <div class="code-block config-example">
        <code>const dynamo  = session.client('dynamodb');
const sqs     = session.client('sqs');
const s3      = session.client('s3');
const sns     = session.client('sns');
const ssm     = session.client('ssm');
const secrets = session.client('secretsmanager');
const sfn     = session.client('stepfunctions');

const queueUrl = session.queueUrl('OrderQueue');  // local SQS URL
const port     = session.portFor('dynamodb');      // port number

await session.reset();  // clear all tables, queues, buckets</code>
      </div>
    </div>
  </section>

  <!-- Resource Helpers -->
  <section class="section section-alt">
    <div class="container">
      <h2>Resource Helpers</h2>
      <p class="section-lead">Async helpers with built-in assertion methods. Skip the boilerplate.</p>

      <h3 class="section-subheading section-subheading--primary">DynamoDB</h3>
      <div class="code-block config-example">
        <code>const table = session.dynamodb('Orders');

await table.put({ id: { S: '1' }, status: { S: 'pending' } });
const item  = await table.get({ id: { S: '1' } });
await table.delete({ id: { S: '1' } });
const items = await table.scan();

await table.assertItemExists({ id: { S: '1' } });  // returns item
await table.assertItemCount(5);</code>
      </div>

      <h3 class="section-subheading section-subheading--primary">SQS</h3>
      <div class="code-block config-example">
        <code>const queue = session.sqs('OrderQueue');

await queue.send({ orderId: '42', total: 99.99 });  // object → JSON
await queue.send('plain text message');

const messages = await queue.receive({ maxMessages: 10 });
await queue.purge();

await queue.assertMessageCount(3);
console.log(queue.url);  // http://localhost:.../OrderQueue</code>
      </div>

      <h3 class="section-subheading section-subheading--primary">S3</h3>
      <div class="code-block config-example">
        <code>const bucket = session.s3('ReceiptsBucket');

await bucket.put('receipts/001.pdf', Buffer.from('PDF bytes'));
await bucket.put('config.json', JSON.stringify({ key: 'value' }));

const data = await bucket.get('receipts/001.pdf');      // Buffer
const text = await bucket.getText('config.json');       // string
const keys = await bucket.listKeys({ prefix: 'receipts/' });
await bucket.delete('config.json');

await bucket.assertObjectExists('receipts/001.pdf');
await bucket.assertObjectCount({ expected: 5, prefix: 'receipts/' });</code>
      </div>
    </div>
  </section>

  <!-- Faking -->
  <section class="section">
    <div class="container">
      <h2>Operation Faking</h2>
      <p class="section-lead">Override any AWS operation response with a fluent builder. No changes to application code needed.</p>

      <div class="code-block config-example">
        <code>// Inject throttling
await session.fake('dynamodb').operation('PutItem').respond({
  status: 400,
  body: { __type: 'ProvisionedThroughputExceededException' },
});

// Add artificial latency
await session.fake('sqs').operation('SendMessage').respond({
  status: 200,
  delayMs: 500,
});

// Clear all fakes for a service
await session.fake('dynamodb').clear();</code>
      </div>
    </div>
  </section>

  <!-- Chaos -->
  <section class="section section-alt">
    <div class="container">
      <h2>Chaos Engineering</h2>
      <p class="section-lead">Inject failure conditions programmatically to verify your application handles them gracefully.</p>

      <div class="code-block config-example">
        <code>await session.chaos('dynamodb').errorRate(0.3).latency({ minMs: 50, maxMs: 200 }).apply();
await session.chaos('sqs').connectionResetRate(0.1).timeoutRate(0.05).apply();
await session.chaos('dynamodb').clear();</code>
      </div>
    </div>
  </section>

  <!-- IAM -->
  <section class="section">
    <div class="container">
      <h2>IAM Authorization</h2>
      <p class="section-lead">Switch IAM modes and define named identities with inline policies to test authorization behaviour.</p>

      <div class="code-block config-example">
        <code>await session.iam.mode('enforce').apply();
await session.iam.mode('audit').apply();
await session.iam.mode('disabled').apply();  // default

await session.iam.defaultIdentity('service-account').apply();

await session.iam
  .identity('readonly')
  .allow(['dynamodb:GetItem', 'dynamodb:Scan'])
  .apply();</code>
      </div>
    </div>
  </section>

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