都道府県の配列データソース

{"北海道","青森県","岩手県","宮城県","秋田県","山形県","福島県",
"茨城県","栃木県","群馬県","埼玉県","千葉県","東京都","神奈川県",
"新潟県","富山県","石川県","福井県","山梨県","長野県","岐阜県",
"静岡県","愛知県","三重県","滋賀県","京都府","大阪府","兵庫県",
"奈良県","和歌山県","鳥取県","島根県","岡山県","広島県","山口県",
"徳島県","香川県","愛媛県","高知県","福岡県","佐賀県","長崎県",
"熊本県","大分県","宮崎県","鹿児島県","沖縄県"
};

contentfulにて

contentfulのバリデーションに都道府県をセットしたい事がありました。
その時のdev-toolに流したjsも貼っておきます。

const add = document.querySelector("#addPredefinedValue")
const ev = document.createEvent('Events');
ev.initEvent('keydown', true, true);
ev.keyCode = 13;
ev.which = 13;
ev.charCode = 13;
ev.key = 'Enter';
ev.code = 'Enter';

["北海道","青森県","岩手県","宮城県","秋田県","山形県","福島県",
"茨城県","栃木県","群馬県","埼玉県","千葉県","東京都","神奈川県",
"新潟県","富山県","石川県","福井県","山梨県","長野県","岐阜県",
"静岡県","愛知県","三重県","滋賀県","京都府","大阪府","兵庫県",
"奈良県","和歌山県","鳥取県","島根県","岡山県","広島県","山口県",
"徳島県","香川県","愛媛県","高知県","福岡県","佐賀県","長崎県",
"熊本県","大分県","宮崎県","鹿児島県","沖縄県"].map(pre => {
  add.value=pre;
  add.dispatchEvent(ev);
});