如何在JavaScript中使用switch
[英]How to use switch in JavaScript
问题描述
I have been trying to make a password generator and I have this code and it is returning "undefined" not a character. 
我一直在尝试制作一个密码生成器，并且我有这段代码，它返回的是“未定义”而不是字符。 The code is supposed to return 16 characters with numbers, lower and upper characters. 该代码应该返回带数字的16个字符，分别包含大写和小写。 I want to have this so that I don't have to worry about making my own passwords anymore. 我想拥有它，这样我就不必担心自己制作密码了。
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>PassGen</title> <script> function getRandomInt(min, max) { return Math.floor(Math.random() * (max - min + 1)) + min; } function num2lett(num) { switch (num) { case (num > 36): return String.fromCharCode(577 + num - 35); break; case (num > 10 && num < 37): return String.fromCharCode(97 + num - 11); break; case (num == 10): return "0"; break; case (num < 10): return "" + num; break; } } function uuidMake() { var uuid = ""; for (u = 0; u < 16; u++) { randNum = getRandomInt(0, 62); uuid += num2lett(randNum); } document.getElementById("password").innerHTML = uuid; } </script> <style> @font-face { font-family: "uuid_font"; src: url("Courier Prime Code.ttf") format("TrueType"); } body { background-color: #262626; } #password { font-family: "uuid_font"; text-align: center; font-size: 30px; color: #dddddd; margin-top: 250px; } </style> <body> <p id="password" onclick="uuidMake();">Click Me</p> </body> </html>
4 个解决方案
解决方案1
2 2017-07-30 06:32:53
This isn't a good use case for switch . 这不是switch好用例。 Use if and else statements. 使用if和else语句。
The case s in a switch statement are specific possible values of the expression that you're switch ing on. 该case在A S switch语句是你表达的特定可能值switch荷兰国际集团上。 For instance, one might write something like: 例如，可能会写类似：
switch (n) {
case 1:
// things to do when n is 1
break;
case 3:
case 4:
// things to do when n is 3 or 4
break;
default:
// things to do when n is neither 1, 3, nor 4
}
A case statement cannot be a range of values. case语句不能是值的范围。 Using an expression as a case is not recommended, either -- it isn't invalid , but it will probably not do what you expect either. 也不建议将表达式用作case ，因为它不是无效的 ，但也可能不会达到您的期望。
解决方案2
1 已采纳 2017-07-30 06:32:29
You can't use case statements like if else so just use if else condition that will work like as following example. 您不能像if else那样使用case语句，而只能使用if else条件，该条件将像以下示例一样工作。
function getRandomInt(min, max) { return Math.floor(Math.random() * (max - min + 1)) + min; } function num2lett(num) { if (num > 36) return String.fromCharCode(577 + num - 35); else if (num > 10 && num < 37) return String.fromCharCode(97 + num - 11); else if (num == 10) return "0"; else if (num < 10) return "" + num; } function uuidMake() { var uuid = ""; for (u = 0; u < 16; u++) { randNum = getRandomInt(0, 62); uuid += num2lett(randNum); } document.getElementById("password").innerHTML = uuid; }
@font-face { font-family: "uuid_font"; src: url("Courier Prime Code.ttf") format("TrueType"); } body { background-color: #262626; } #password { font-family: "uuid_font"; text-align: center; font-size: 30px; color: #dddddd; margin-top: 250px; }
<p id="password" onclick="uuidMake();">Click Me</p>
What is your algorithm I don't know so I am just converted your algorithm to if else 我不知道您的算法是什么，所以我只是将您的算法转换为
解决方案3
1 2017-07-30 06:32:31
In the switch block, you have written conditional statements in the case . 在switch块中，您编写了case条件语句。
You can't use conditional statements in the switch block. 您不能在switch块中使用条件语句。 Hence in your case none of the case are executing. 因此，在您的情况下，所有case都没有执行。 As you don't have a default block, your function doesn't returns anything, which in case of javascript is undefined . 由于您没有default块，因此您的函数不会返回任何内容（如果使用javascript，则该函数undefined 。 Hence you are getting undefined 因此，您变得undefined
解决方案4
0 2017-07-30 07:17:11
You can alter switch statement to make it work. 您可以更改switch语句以使其起作用。 Pass 'true' in switch and remove parentheses from case condition 在开关中传递“ true”并从大小写条件中删除括号
switch (true) {
case num > 36:
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