Array.isArray, Array.prototype.map and Array.prototype.forEachVarious jQuery methods have native equivalents and are supported by all grade A browsers in MediaWiki, yet in core we continue to use jQuery methods
We should modernize this code and enforce usage of native JavaScript via eslint going forward.
= Acceptance criteria
For purpose of Google-Code-In this can be separated into tasks if necessary.
[] eslint is set up to warn against violations (https://gerrit.wikimedia.org/r/449670)
[] All $.isArray -> Array.isArray
[] All $.map -> Array.prototype.map
[] All $.each -> Array.prototype.forEach
[] All $.grep -> Array.prototype.filter
[] All $.inArray -> Array.prototype.indexOf
[] All $.trim -> String.prototype.trim
[] eslint is updated to error rather than warn
[] The wikimedia eslint config is updated (https://github.com/wikimedia/eslint-config-wikimedia) so that other extensions and skins are made to adhere to this rule.