Auto approve Pull Request Server on Azure DevOps

Question

I am writing a server on express js in oder to auto approve pull requests under specific circumstances on Azure DevOps. Here is part of my code :

let connection = new azdev.WebApi(orgUrl, authHandler);

connection.getGitApi().then(gitApi => {
        // retrieve PR
        gitApi.getPullRequestCommits(repositoryId, pullRequestId).then(result => {
            connection.getGitApi().then(git => {
                // retrieve all changes of PR
                git.getChanges(result[0].commitId, repositoryId).then(result => {
                    ...
                }
            }
         }
}

Now, I check some conditions on the changes and if this conditions are filled, I want to approve the PR. How can I do that? I can not find any API to control the approve or reject of a PR. Thank you in advance.