ERROR: CLASS ‘WP_SESSION_TOKENS’ NOT FOUND

I use a childtheme based on twentyfourteen.
I got two javascript errors:
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in file preveter-index.php, line 177

var e = document.getElementsByTagName(‘body’)[0];
e.setAttribute(‘unselectable’,’on’);
This yields error: e is undefined.
I replaced it with:

(function($) {
$(“body”).prop(“unselectable”, “on”);
})(jQuery);
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in preventer-index.php, line 128:
$(document).keydown(function(event) {
yield error: $ is not a function.
I replaced it with:
jQuery(document).keydown(function(event) {
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Now it’s fault free