What's the effect of adding 'return false' to a click event listener?

Question

Many times I\'ve seen links like these in HTML pages:

Click here !

Answer 1

Return false will stop the hyperlink being followed after the javascript has run. This is useful for unobtrusive javascript that degrades gracefully - for example, you could have a thumbnail image that uses javascript to open a pop-up of the full-sized image. When javascript is turned off or the image is middle-clicked (opened in a new tab) this ignores the onClick event and just opens the image as a full-sized image normally.

If return false were not specified, the image would both launch the pop-up and open the image normally. Some people instead of using return false use javascript as the href attribute, but this means that when javascript is disabled the link will do nothing.