Use `wp_json_encode()` to safely render text inside `script` tag

[hbhalodia]

What?

• The issue is while adding the text inside the javascript using innertext the text is not escaped via wp_json_encode() which can result into malicious injection or can be a syntax error in other languages.

Given this existing code:

button.innerText = '<?php esc_html_e( 'Preview', 'preview-revisions' ); ?>';

It could be that a translation string incorporates an apostrophe, either because the language uses apostrophes:

Which would result in a syntax error here:

button.innerText = 'mua'i va'aiga';
// --------------------^

[hbhalodia]

This issue is done in PR - https://github.com/rtCamp/wordpress-preview-revisions/pull/1

[hbhalodia]

The issue is successfully tested and merged into master.