diff --git a/src/api.ts b/src/api.ts
index e907378b..5debb68d 100644
--- a/src/api.ts
+++ b/src/api.ts
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2018 StApps
+ * Copyright (C) 2018, 2019 StApps
  * This program is free software: you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the Free
  * Software Foundation, version 3.
@@ -19,15 +19,23 @@ import {
   Branch,
   Group,
   Issue,
+  IssueState,
   Label,
   Member,
+  MembershipScope,
   MergeRequest,
+  MergeRequestApproval,
+  MergeRequestState,
   Milestone,
   Project,
+  Scope,
   Tag,
   TreeFile,
 } from './types';
 
+/**
+ * Instance of logger
+ */
 export const logger = new Logger();
 
 /**
@@ -59,8 +67,8 @@ export interface ApiRequestOptions {
  */
 export interface ApiGetIssuesOptions {
   groupId?: number;
-  milestone?: 'Meeting' | 'Backlog' | 'No Milestone';
-  state?: 'opened' | 'closed';
+  milestone?: 'Backlog' | 'No Milestone';
+  state?: IssueState;
 }
 
 /**
@@ -102,17 +110,17 @@ export class Api {
   /**
    * Add member to a group or a project
    *
-   * @param scope Scope of the ID
+   * @param scope MembershipScope of the ID
    * @param id ID of the group or project
    * @param userId ID of the user
    * @param accessLevel Access level for the new member in the scope
    */
-  public addMember(scope: 'groups' | 'projects',
+  public addMember(scope: MembershipScope,
                    id: number,
                    userId: number,
                    accessLevel: AccessLevel): Promise<Member> {
     return this.makeGitLabAPIRequest(
-      scope + '/' + id + '/members',
+      `${scope}/${id}/members`,
       {
         data: {
           access_level: accessLevel,
@@ -132,7 +140,7 @@ export class Api {
    */
   public createIssue(projectId: number, title: string, description: string): Promise<Issue> {
     return this.makeGitLabAPIRequest(
-      'projects/' + projectId + '/issues',
+      `projects/${projectId}/issues`,
       {
         data: {
           description: description,
@@ -157,7 +165,7 @@ export class Api {
     }
 
     return this.makeGitLabAPIRequest(
-      'projects/' + projectId + '/labels',
+      `projects/${projectId}/labels`,
       {
         data: {
           color: color,
@@ -215,12 +223,12 @@ export class Api {
   /**
    * Delete a member from a group or a project
    *
-   * @param scope Scope of the ID
+   * @param scope MembershipScope of the ID
    * @param id ID of the group or project
    * @param userId ID of the user
    */
-  public deleteMember(scope: 'groups' | 'projects', id: number, userId: number): Promise<void> {
-    return this.makeGitLabAPIRequest(scope + '/' + id + '/members/' + userId, {method: 'DELETE'});
+  public deleteMember(scope: MembershipScope, id: number, userId: number): Promise<void> {
+    return this.makeGitLabAPIRequest(`${scope}/${id}/members/${userId}`, {method: 'DELETE'});
   }
 
   /**
@@ -236,7 +244,7 @@ export class Api {
     }
 
     return this.makeGitLabAPIRequest(
-      'projects/' + projectId + '/labels',
+      `projects/${projectId}/labels`,
       {
         data: {
           color: newValues.color,
@@ -252,17 +260,17 @@ export class Api {
   /**
    * Edit member in a group or a project
    *
-   * @param scope Scope of the ID
+   * @param scope MembershipScope of the ID
    * @param id ID of the group or project
    * @param userId ID of the user
    * @param accessLevel Access level for the member in the scope
    */
-  public editMember(scope: 'groups' | 'projects',
+  public editMember(scope: MembershipScope,
                     id: number,
                     userId: number,
                     accessLevel: AccessLevel): Promise<Member> {
     return this.makeGitLabAPIRequest(
-      scope + '/' + id + '/members',
+      `${scope}/${id}/members`,
       {
         data: {
           access_level: accessLevel,
@@ -279,7 +287,7 @@ export class Api {
    * @param projectId Project ID to get branches for
    */
   public getBranchesForProject(projectId: number): Promise<Branch[]> {
-    return this.makeGitLabAPIRequest('projects/' + projectId + '/repository/branches');
+    return this.makeGitLabAPIRequest(`projects/${projectId}/repository/branches`);
   }
 
   /**
@@ -291,7 +299,7 @@ export class Api {
    */
   public getFile(projectId: number, filePath: string, commitish: string): Promise<any> {
     return this.makeGitLabAPIRequest(
-      'projects/' + projectId + '/repository/files/' +
+      `projects/${projectId}/repository/files/` +
       encodeURIComponent(filePath).replace('.', '%2E') + '/raw?ref=' + encodeURIComponent(commitish),
     );
   }
@@ -302,7 +310,7 @@ export class Api {
    * @param projectId ID of the project
    */
   public getFileList(projectId: number): Promise<TreeFile[]> {
-    return this.makeGitLabAPIRequest('projects/' + projectId + '/repository/tree');
+    return this.makeGitLabAPIRequest(`projects/${projectId}/repository/tree`);
   }
 
   /**
@@ -375,7 +383,7 @@ export class Api {
    * @param projectId Project ID to get milestones for
    */
   public getMilestonesForProject(projectId: number): Promise<Milestone[]> {
-    return this.makeGitLabAPIRequest('projects/' + projectId + '/milestones');
+    return this.makeGitLabAPIRequest(`projects/${projectId}/milestones`);
   }
 
   /**
@@ -384,7 +392,7 @@ export class Api {
    * @param groupId Group ID to get projects for
    */
   public getProjectsForGroup(groupId: number): Promise<Project[]> {
-    return this.makeGitLabAPIRequest('groups/' + groupId + '/projects');
+    return this.makeGitLabAPIRequest(`groups/${groupId}/projects`);
   }
 
   /**
@@ -403,7 +411,7 @@ export class Api {
    */
   public getTags(projectId: number): Promise<Tag[]> {
     return this.makeGitLabAPIRequest(
-      'projects/' + projectId + '/repository/tags',
+      `projects/${projectId}/repository/tags`,
     );
   }
 
@@ -502,8 +510,8 @@ export class Api {
    */
   public protectBranch(projectId: number, branch: string): Promise<Branch> {
     return this.makeGitLabAPIRequest(
-      'projects/' + projectId + '/repository/branches/' + branch + '/protect' +
-      '?developers_can_push=false&developers_can_merge=false',
+      /* tslint:disable-next-line:max-line-length */
+      `projects/${projectId}/repository/branches/${branch}/protect?developers_can_push=false&developers_can_merge=false`,
       {
         method: 'PUT',
       },
@@ -516,9 +524,9 @@ export class Api {
    * @param issue Issue to set milestone for
    * @param userId ID of the milestone to set for the issue
    */
-  public setAssigneeForIssue(issue: any, userId: number): Promise<Issue> {
+  public setAssigneeForIssue(issue: Issue, userId: number): Promise<Issue> {
     return this.makeGitLabAPIRequest(
-      'projects/' + issue.project_id + '/issues/' + issue.iid + '?assignee_ids=' + userId,
+      `projects/${issue.project_id}/issues/${issue.iid}?assignee_ids=${userId}`,
       {
         method: 'PUT',
       },
@@ -531,10 +539,10 @@ export class Api {
    * @param issue Issue to set milestone for
    * @param milestoneId ID of the milestone to set for the issue
    */
-  public setMilestoneForIssue(issue: any, milestoneId: number): Promise<Issue> {
+  public setMilestoneForIssue(issue: Issue, milestoneId: number): Promise<Issue> {
     if (milestoneId === null) {
       return this.makeGitLabAPIRequest(
-        'projects/' + issue.project_id + '/issues/' + issue.iid + '?milestone_id=',
+        `projects/${issue.project_id}/issues/${issue.iid}?milestone_id=`,
         {
           method: 'PUT',
         },
@@ -542,7 +550,7 @@ export class Api {
     }
 
     return this.makeGitLabAPIRequest(
-      'projects/' + issue.project_id + '/issues/' + issue.iid + '?milestone_id=' + milestoneId,
+      `projects/${issue.project_id}/issues/${issue.iid}?milestone_id=${milestoneId}`,
       {
         method: 'PUT',
       },