I am trying to migrate my application in Meteor 1.4 and currently it is on meteor 1.2 so I should go as defined in below link or change my complete code as per meteor doc.
What’s the question? Just follow the article
Follow the guide, not an article. You can try to go to 1.4 immediately or take it as a 2 step process:
First: https://guide.meteor.com/1.3-migration.html
Then when stable: https://guide.meteor.com/1.4-migration.html
You will need to read and check both change overviews so you can see where you may encounter issues.
You do not have to upgrade to the imports structure etc. packages still work same as blaze and the other existing meteor packages. The 2 linked guides show clearly where you may encounter issues and how to resolve them.
We did not run into major issues when upgrading at all by following those.
I upgraded from 1.1 to 1.2, then from 1.2 to 1.3 without issues recently. But I ran into issues when trying to upgrade to 1.4.1.1. I went back to 1.3.5.1 and am waiting for the next version bump before trying again. I won’t go into it here, but make sure you read about issues on 1.4.1.1 and take them into account before making the jump.
Think of the article as a blogged experience of upgrading Meteor to 1.4, following a TDD approach. You can start with the official guide, then supplement with the article if needed.