为什么使用 OOP 时字符串旁边有一个“未定义”？
我目前正在使用 OOP 来显示烹饪食谱。一切都很好，除了我使用该document.write方法时。当显示price. 这是我的代码：
<html>
<body>
<p id = "p"></p>
<script>
function Recipe(name, ingredients, price) {
this.name = name;
this.ingredients = ingredients;
this.price = price;
}
function describe(name, ingredients, price) {
document.write("<h2> Recipe name: " + name + "</h2> Ingredients: " + ingredients + "<br />Price: " + price);
}
var instantRamen = new Recipe("Ramen", "Ramen noodles, hot water, salt, (optional) green pepper", "$2.00");
var Bagel = new Recipe("Ham and cheese bagel", "Bagel (preferably an everything bagel), ham, cheese (of any type), pepper (just a little)", "$6.00");
document.write(describe(instantRamen.name, instantRamen.ingredients, instantRamen.price));
document.write(describe(Bagel.name, Bagel.ingredients, Bagel.price));
</script>
</body>
</html>
预期结果将类似于“食谱名称：拉面（换行）配料：拉面、热水、盐、（可选）青椒（换行）价格：2.00 美元”，但价格变为“2.00 美元未定义”。其他一切都有效。
我最初认为创建instantRamenandBagel实例时有问题，所以我尝试更改一些语法但无济于事。
绝地无双3回答
-
桃花长相依
您可以return像这样使用您的功能。因为您没有返回任何值。那西undefinedfunction Recipe(name, ingredients, price) { this.name = name; this.ingredients = ingredients; this.price = price;}function describe(name, ingredients, price) { return "<h2> Recipe name: " + name + "</h2> Ingredients: " + ingredients + "<br />Price: " + price;}var instantRamen = new Recipe("Ramen", "Ramen noodles, hot water, salt, (optional) green pepper", "$2.00");var Bagel = new Recipe("Ham and cheese bagel", "Bagel (preferably an everything bagel), ham, cheese (of any type), pepper (just a little)", "$6.00");document.write(describe(instantRamen.name, instantRamen.ingredients, instantRamen.price));document.write(describe(Bagel.name, Bagel.ingredients, Bagel.price));<html> <body> <p id = "p"></p></body></html>我已经删除document.write了return字符串。 -
天涯尽头无女友
问题是你在函数describe内部调用document.write函数。它写undefined因为 describe 什么都不返回。发生的事情是：首先，describe函数在文档中写入 html 文本。然后，您尝试describe在文档中编写函数的返回。您不需要将describe函数放在里面，document.write.只需使用您想要的参数调用它即可。 -
慕尼黑5688855
现在它的工作<html> <body> <p id = "p"></p><script>function Recipe(name, ingredients, price) { this.name = name; this.ingredients = ingredients; this.price = price;}function describe(name, ingredients, price) { document.write("<h2> Recipe name: " + name + "</h2> Ingredients: " + ingredients + "<br />Price: " + price );}var instantRamen = new Recipe("Ramen", "Ramen noodles, hot water, salt, (optional) green pepper", "$2.00");var Bagel = new Recipe("Ham and cheese bagel", "Bagel (preferably an everything bagel), ham, cheese (of any type), pepper (just a little)", "$6.00");//editeddescribe(instantRamen.name, instantRamen.ingredients, instantRamen.price);describe(Bagel.name, Bagel.ingredients, Bagel.price);document.getElementById("p").innerHTML = "Your browser version is " + navigator.appVersion;</script></body></html>
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JavaScript