Submitting search form (mini) with enter key fires event handlers bound by jquery twice

[gelanivishal]

Original Pull Request

#15340

Description

When submitting the search form in the header with the enter key on the keyboard, event handlers that were bound to the form submit (through jQuery) are fired twice.

Fixed Issues (if relevant)

1. Submitting search form (mini) with enter key fires event handlers bound by jquery twice #13793: Submitting search form (mini) with enter key fires event handlers bound by jquery twice

Manual testing scenarios

1. Create a javascript which adds an event handler to the form submit
2. $('#search_mini_form').on('submit', function(e) {
   console.log('listening for form submit');
   });
3. Submit the search form in the header with a value by pressing the enter button

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[orlangur]

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