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三項演算子の説明と三項演算子の例題

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今回はJavaScriptで使われてる三項演算子の説明と、HTML上で入力した数字が奇数か偶数かを判断するページを作ってみます。

#三項演算子とは?
「?」と「:」を組見合わせて、if~else文のような処理を簡略化したものです。

#書き方

条件式式1式2

ページの制作

JavaScriptをHTMLに繋げる方法を知ってる前提で説明します。

JavaScriptのソース

function checkEven() {
  var v = document.getElementById("number").value;
  var r = document.getElementById("result");
  if(v.length == 0) {
    r.textContent = "何かの入力値が必要です";
  } else if(isNaN(v)){
    r.textContent = v + "は数字ではありません";
  } else {
    r.textContent = (v%2==0) ? "偶数です":"奇数です";
  }   
}

HTMLのソース

<h1>奇数か偶数かを判断します。</h1>
<input id="number" />
<button onclick="checkEven()">入力判定</button>
<p id="result"></p>

引用 : Dripcoke

初めてのJavascript-(8)-制御式

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