以下是使用AWS API Gateway，Lambda和JavaScript CORS解决跨域问题的示例代码：

1. AWS API Gateway配置CORS

在AWS API Gateway中，你可以通过配置CORS来允许特定的源访问你的API。你可以在API Gateway的资源中设置CORS。

Resources:
  MyApiGateway:
    Type: AWS::ApiGateway::RestApi
    Properties:
      Name: MyApiGateway

  MyApiGatewayResource:
    Type: AWS::ApiGateway::Resource
    Properties:
      RestApiId: !Ref MyApiGateway
      ParentId: !GetAtt MyApiGateway.RootResourceId
      PathPart: myresource

  MyApiGatewayMethod:
    Type: AWS::ApiGateway::Method
    Properties:
      RestApiId: !Ref MyApiGateway
      ResourceId: !Ref MyApiGatewayResource
      HttpMethod: GET
      AuthorizationType: NONE
      Integration:
        Type: AWS
        IntegrationHttpMethod: POST
        Uri: !Sub
          - arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${LambdaFunction.Arn}/invocations
          - LambdaFunction: !Ref LambdaFunction
      MethodResponses:
        - StatusCode: 200
      RequestParameters:
        - MethodRequestParameterName: integration.request.header.Origin
          Required: true

  MyApiGatewayOptionsMethod:
    Type: AWS::ApiGateway::Method
    Properties:
      RestApiId: !Ref MyApiGateway
      ResourceId: !Ref MyApiGatewayResource
      HttpMethod: OPTIONS
      AuthorizationType: NONE
      Integration:
        Type: MOCK
        IntegrationResponses:
          - StatusCode: 200
            ResponseParameters:
              method.response.header.Access-Control-Allow-Headers: "'Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security-Token'"
              method.response.header.Access-Control-Allow-Origin: "'*'"
              method.response.header.Access-Control-Allow-Methods: "'GET,OPTIONS'"
      MethodResponses:
        - StatusCode: 200
          ResponseParameters:
            method.response.header.Access-Control-Allow-Headers: true
            method.response.header.Access-Control-Allow-Methods: true
            method.response.header.Access-Control-Allow-Origin: true

2. Lambda函数设置CORS HTTP响应头

在Lambda函数中，你可以在HTTP响应头中设置CORS头部信息，以允许跨域访问。

exports.handler = async (event) => {
    const response = {
        statusCode: 200,
        headers: {
            'Access-Control-Allow-Origin': '*',
            'Access-Control-Allow-Headers': 'Content-Type',
            'Access-Control-Allow-Methods': 'GET, POST, PUT, DELETE'
        },
        body: JSON.stringify('Hello from Lambda!')
    };
    return response;
};

3. JavaScript中的CORS请求

在JavaScript中，你可以使用XMLHttpRequest或Fetch API来进行CORS请求。

使用XMLHttpRequest示例：

const xhr = new XMLHttpRequest();
xhr.open('GET', 'https://api.example.com/myresource', true);
xhr.setRequestHeader('Content-Type', 'application/json');
xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
        const response = JSON.parse(xhr.responseText);
        console.log(response);
    }
};
xhr.send();

使用Fetch API示例：

fetch('https://api.example.com/myresource', {
    method: 'GET',
    headers: {
        'Content-Type': 'application/json'
    }
})
.then(response => response.json())
.then(data => console.log(data))
.catch(error => console.error(error));

以上是使用AWS API Gateway，Lambda和JavaScript CORS解决跨域问题的示例代码。请注意，示例代码中的API网关和Lambda函数的配置需要根据你的具体情况进行调整。