Result

jQuery

//フォーカスイベント
$("#s").focus(function() {
     //フォーカス時はvalueを空にする
    if (this.value == this.defaultValue) {
        this.value = "";
    }
     //フォーカスが離れたらデフォルト状態
}).blur(function() {
    if (!this.value.length) {
        this.value = this.defaultValue;
    }
});

html

<input type="text" name="example" id="s" value="search"><input type="submit" value="search" class="btn">

via

Unobtrusive “clear searchfield on focus”

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Warning: include(): Failed opening '/home/youhei0828/kachibito.net/public_html/wp-content/themes/cocoon-master/my-php/jquery-other-snippets.php' for inclusion (include_path='.:/opt/php-8.1.29/data/pear') in /home/youhei0828/kachibito.net/public_html/wp-content/themes/kachibito7_with_cocoon_child/functions-module/shortcode/add-post-myphp.php on line 7