How to use the azure-devops-node-api/WebApi.WebApi function in azure-devops-node-api

var buildId: number = null;
        var buildVersionToDownload: string = tl.getInput("buildVersionToDownload", false);
        var allowPartiallySucceededBuilds: boolean = tl.getBoolInput("allowPartiallySucceededBuilds", false);
        var branchName: string = tl.getInput("branchName", false);;
        var downloadPath: string = tl.getInput("downloadPath", true);
        var downloadType: string = tl.getInput("downloadType", true);
        var tagFiltersInput: string = tl.getInput("tags", false);
        var tagFilters = [];
        if (!!tagFiltersInput) {
            tagFilters = tagFiltersInput.split(",");
        }

        var endpointUrl: string = tl.getVariable("System.TeamFoundationCollectionUri");
        var accessToken: string = tl.getEndpointAuthorizationParameter('SYSTEMVSSCONNECTION', 'AccessToken', false);
        var credentialHandler: IRequestHandler = getHandlerFromToken(accessToken);
        var webApi: WebApi = new WebApi(endpointUrl, credentialHandler);
        var retryLimit = parseInt(tl.getVariable("VSTS_HTTP_RETRY")) ? parseInt(tl.getVariable("VSTS_HTTP_RETRY")) : 4;

        var templatePath: string = path.join(__dirname, 'vsts.handlebars.txt');
        var buildApi: IBuildApi = await webApi.getBuildApi();
        var artifacts = [];

        if (isCurrentBuild) {
            projectId = tl.getVariable("System.TeamProjectId");
            definitionId = '';
            buildId = parseInt(tl.getVariable("Build.BuildId"));
        }
        else {
            var releaseAlias: string = tl.getVariable("release.triggeringartifact.alias");
            var triggeringBuildFound: boolean = false;
            definitionIdSpecified = tl.getInput("definition", true);
            if (isSpecificBuildWithTriggering) {

public static async getRestClients(accountUrl: string, PAT: string): Promise {
        const authHandler = vsts.getPersonalAccessTokenHandler(PAT);
        const vstsWebApi = new vsts.WebApi(accountUrl, authHandler);
        try {
            return {
                "witApi": await vstsWebApi.getWorkItemTrackingApi(),
                "witProcessApi": await vstsWebApi.getWorkItemTrackingProcessApi(),
                "witProcessDefinitionApi": await vstsWebApi.getWorkItemTrackingProcessDefinitionApi(),
            }
        }
        catch (error) {
            throw new KnownError(`Failed to connect to account '${accountUrl}' using personal access token '' provided, check url and token.`);
        }
    }