CDTJS is an interactive web app for generating constrained Delaunay triangulations of 2D points, written in JavaScript.
Check out the app here.
How to use
 Insert a set of 2D points to triangulate.
 Random: A random distribution of points may be added by entering the required number of points and clicking the “Generate random vertices” button. The points can be sampled from a uniform or standard normal distribution.
 Import from file: Points may also be imported from a file using the button under “Load vertices from file”. The x and y coordinates of each point should be space or commaseparated, and each point should exist on its own line.
 Manual entry: Directly add or modify points using the textbox under “Vertex list”, and click the “Reload input data” button.
 Specify the set of edges to constrain, if any.
 Random: Click the “Generate random edge constraints” button to randomly generate the specified number of edge constraints.
 Import from file: Edge constraints can also be imported from a file using the button under “Load constrained edges from file”. Each edge should be specified by the indices to its two endpoints in the vertex list. The vertex indices use 0based indexing, and should be space or commaseparated.
 Manual entry: Directly add or modify edge constraints using the textbox under “Constrained edge list”, and click the “Reload input data” button.

Click the “Triangulate!” button to generate the constrained Delaunay triangulation.
 Explore!
 Click on the visualization to see more information about the points and triangles.
 Locate and visualize a particular point or triangle by its index.
 The indices to the three vertices of each triangle are printed in the last textbox of the control panel.
Performance
Some benchmark results obtained on an Intel Core i74712HQ (2.3 GHz), running Google Chrome v70.0 (JavaScript V8).
N = 100  N = 1000  N = 10,000  N = 100,000  

Random points  uniform distribution, no edge constraints  1ms  5ms  41ms  570ms 
Random points  normal distribution, no edge constraints  1ms  5ms  52ms  837ms 
Random points  uniform distribution, 0.01N edge constraints  2ms  5ms  65ms  1.6s 
Random points  uniform distribution, 0.1N edge constraints  2ms  8ms  232ms  26.5s 
References
The algorithms implemented here are based on the following papers:
 A fast algorithm for generating constrained Delaunay triangulations, S.W. Sloan, Computers & Structures, 1993.
 A robust efficient algorithm for point location in triangulations, P.J.C. Brown and C.T. Faigle, Technical Report, University of Cambridge, 1997.