Question

您好我是编码的新手，我想尝试一下我学到了多少（不是那么多）所以我做到了：

var Name = prompt('What is your name?') 
var Name
var Age  = prompt('What is your age?') 
var Age 
const RealAge = 2018 - Age
if (Name && RealAge) {
    console.log("Hello " + Name + " you were born in " + RealAge + ' ...')
} else if (typeof Name == 'undefined') {
    console.log("Please insert your name")
} else if (typeof Age == 'undefined' ) {
    console.log("Please insert your age")
}

我想知道怎么制作console.log如果你把第一个提示留空，请说“请插入你的名字”，如果第二个提示留空，请说“请插入你的年龄”。

我很抱歉，如果这是一个愚蠢的问题，但我刚刚开始2天前，我将非常感谢你的帮助：）

Answer 1

if (Name && RealAge) {
    console.log("Hello " + Name + " you were born in " + RealAge + ' ...')
} else if (!Name) {
    console.log("Please insert your name")
} else if (!Age) {
        console.log("Please insert your age")
}

如果值为falsy（未定义，null，空字符串），

!Name将计算为true。

此外，正如Frederico所提到的，最好在进行任何计算之前检查这些值：

var Name = prompt('What is your name?') 
var Name
var Age  = prompt('What is your age?') 
var Age 
if (!Name) {
    console.log("Please insert your name")
} else if (!Age) {
    console.log("Please insert your age")
} else {
    const RealAge = 2018 - +Age;
    console.log("Hello " + Name + " you were born in " + RealAge + ' ...')
}

如果你需要知道什么时候都没有输入：

var Name = prompt('What is your name?') 
var Name
var Age  = prompt('What is your age?') 
var Age 
if (!Name) {
    if (!Age) {
        console.log("Please insert your name and age")
    }
    else {
        console.log("Please insert your name")
    }
} else if (!Age) {
    console.log("Please insert your age")
} else {
    const RealAge = 2018 - +Age;
    console.log("Hello " + Name + " you were born in " + RealAge + ' ...')
}

Answer 2

您不会一次又一次地声明变量。此外，如果用户未在提示中输入任何内容，则其值为""且未定义。所以请查看=== ""。

var Name = prompt('What is your name?'); 
var Age  = prompt('What is your age?'); 
const RealAge = 2018 - +Age;
if (Name && RealAge) {
    console.log("Hello " + Name + " you were born in " + RealAge + ' ...')
} else if (Name === '') {
    console.log("Please insert your name")
} else if (Age === '' ) {
    console.log("Please insert your age")
}

如何根据是否定义变量来更改console.log（）输出消息

2 个答案: