ajax如何调用wfv,javascript - Display loading text or image when href link is clicked inside div of html ...

I'm making an website with tons of Notes and Books to Download. I would Like to show any image or any Text when Link is Download link is clicked and when request is complete and file starts to Download , then remove the image or Loading Text.

I've gone through lots of forums but couldn't find any solution.

Here is the html File of mine

1. First Semestar

   1. Electronics

      1. Bogart Chapter 8 Solutions

      2. Bogart Digital to Analog Chapter
      3. An Introduction to Error Analysis
      4. Basic of Electronics
      5. Solution from Bogart Book
      6. Least Square Solutions
      7. Estimation of Error

   2. Mathematical Physics

      1. Tutorial One and Two
      2. Tutorial One and Two II
      3. Tutorial 4
      4. Tutorial 3
      5. Curvature and Torison Curves
      6. Arfken Solution
      7. Schaum's tensor Analysis
      8. George B. Arfken, Hans J. Weber, Manual_ Mathematical Methods for Physicists
      9. Schaum's Tensor Calculus
      10. Vector space and Eigen Value
      11. Vector in Functional space
      12. Vector funtional Space
      13. Orothonormal Basis
      14. Linear Vector Space
      15. Linear Transformation
      16. Change of Basis
      17. Operators
      18. Operators

   3. Quantum Mechanics

      1. Binil Sir Lecture ( 1-5 ) From Quantum Spin
      2. Schaum's Series
      3. Basis and Dimension

   4. Classical Mechanics

      1. Non-Linear Dynamics
      2. Goldstein Chp 8 Solutions ( BG Sir Homework )
      3. Goldstein Chp 9 Solutions Handwritten ( BG Sir Homework )
      4. Goldstein Chp 9 Solutions (BG Sir Homework)
      5. Operator formalism of quantum mechanics