defer This Boolean attribute is set to indicate to a browser that the script is meant to be executed after the document has been parsed. Since this feature hasn't yet been implemented by all other major browsers, authors should not assume that the script’s execution will actually be deferred. The defer attribute shouldn't be used on scripts that don't have the src attribute. Since Gecko 1.9.2, the defer attribute is ignored on scripts that don't have the src attribute. However, in Gecko 1.9.1 even inline scripts are deferred if the defer attribute is set.