预先加入“http：//”到不包含“http：//”的URL。 [英] Prepending "http://" to a URL that doesn't already contain "http://"

问题描述

我有一个保存URL的 input 字段，我希望这个保存的输入能够识别变量开始时Http //何时不存在，但是不知道从哪里开始......是否可以只检查一部分字符串？ - 然后有一个函数，如果有必要可以追加？

解决方案

一个简单的解决方案，您需要的是以下内容：

  var prefix ='http：//'; 
 if（s.substr（0，prefix.length）！==前缀）
 {
 s = prefix + s; 
} 
  

然而，有几件事你应该知道...... p>

这里的测试区分大小写。这意味着如果字符串最初是 Http://example.com ，它会将其更改为 http：// Http：//example.com 这可能不是你想要的。你可能也不应该修改任何以 foo：// 开头的字符串，否则你可能会以 http：// https：//为例另一方面，如果您收到一个输入，如 example.com?redirect=http：。 $ b < //othersite.com 那么你可能想要在> http：// 之前加上，所以只需搜索：// 对于一般解决方案可能不够好。

其他方法

• 使用正则表达式：

    if（！s.match （/ ^ [a-zA-Z] +：\ / \ //））
   {
  s ='http：//'s; 
  } 
    




• 使用URI解析库，例如 JS-URI 。
  
  

    if（new URI（s）.scheme === null）
   {
  s ='http：//'s; 
  } 
    

相关问题

> javascript startswith

I have an input field that saves a URL, I'd like this saved input to recognize when "Http//" is absent from the start of the variable but have no idea where to begin... is it possible to check only a portion of a string? - then have a function that will append if necessary?

解决方案

A simple solution for what you want is the following:

var prefix = 'http://';
if (s.substr(0, prefix.length) !== prefix)
{
    s = prefix + s;
}

However there are a few things you should be aware of...

The test here is case-sensitive. This means that if the string is initially Http://example.com this will change it to http://Http://example.com which is probably not what you want. You probably should also not modify any string starting with foo:// otherwise you could end up with something like http://https://example.com.

On the other hand if you receive an input such as example.com?redirect=http://othersite.com then you probably do want to prepend http:// so just searching for :// might not be good enough for a general solution.

Alternative approaches

• Using a regular expression:

  if (!s.match(/^[a-zA-Z]+:\/\//))
  {
      s = 'http://' + s;
  }
  

• Using a URI parsing library such as JS-URI.

  if (new URI(s).scheme === null)
  {
      s = 'http://' + s;
  }
  

Related questions

• Javascript equalsIgnoreCase: case insensitive string comparation
• javascript startswith
• How do I parse a URL into hostname and path in javascript?

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