hint

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const HINT_CLASS = 'hint__show'
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/**
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* @param {number} ms
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* @returns {Promise}
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*/
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const delay = ms => new Promise(resolve => setTimeout(resolve, ms))
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/** @param {HTMLDivElement} hint */
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const show = hint => hint.classList.add(HINT_CLASS)
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/** @param {HTMLDivElement} hint */
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const hide = hint => hint.classList.remove(HINT_CLASS)
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/** @param {HTMLDivElement} hint */
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const showHideHandler = hint => delay(1000)
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  .then(show.bind(null, hint))
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  .then(delay.bind(null, 3000))
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  .then(hide.bind(null, hint))
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document.querySelectorAll('.hint')
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  .forEach(showHideHandler)
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