bootstrap navbar collapse not working code example

Example 1: navbar toggle not working bootstrap 4

You need to put:-

<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
Before all the other js files.

Then it will work.

Working example:- https://jsfiddle.net/mmqhw26j/

Note:- Take care that jQuery core-library/base-library need to be added first and then only any other jQuery file/library can be added

Example 2: bootstrap navbar-inverse not working

Bootstrap have dropped support for bg-inverse.You need to use 
combination of navbar-light bg-light or navbar-dark bg-dark with
nav component. For example:
<nav class="navbar navbar-dark bg-dark">

Example 3: bootstrap 4 navbar-collapse not working angular

<button class="navbar-toggler" type="button" (click)="navbarCollapsed = !navbarCollapsed" [attr.aria-expanded]="!navbarCollapsed" aria-controls="navbarContent" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
</button>

Example 4: bootstrap 4 navbar-collapse not working angular

<div class="collapse navbar-collapse" [ngbCollapse]="navbarCollapsed" id="navbarSupportedContent">