正则表达式字符串以在 Javascript 中不起作用而结束
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Regex string ends with not working in Javascript
提问by Tony_Henrich
I am not very familiar with regex. I was trying to test if a string ends with another string. The code below returns null when I was expecting true. What's wrong with the code?
我对正则表达式不是很熟悉。我试图测试一个字符串是否以另一个字符串结尾。当我期望为 true 时，下面的代码返回 null。代码有什么问题？
var id = "John";
var exists ="blahJohn".match(/id$/);
alert(exists);
回答by CMS
Well, with this approach, you would need to use the RegExpconstructor, to build a regular expression using your idvariable:
好吧，使用这种方法，您需要使用RegExp构造函数，使用您的id变量构建正则表达式：
var id = "John";
var exists = new RegExp(id+"$").test("blahJohn");
alert(exists);
But there are plenty ways to achieve that, for example, you can take the last id.lengthcharacters of the string, and compare it with id:
但是有很多方法可以实现这一点，例如，您可以获取id.length字符串的最后一个字符，并将其与id：
var id = "John";
var exist = "blahJohn".slice(-id.length) == id; // true
回答by James Sumners
You would need to use a RegExp()object to do that, not a literal:
您需要使用RegExp()对象来做到这一点，而不是文字：
var id = "John",
reg = new RegExp(id+"$");
alert( reg.test("blahJon") );
That is, if you do not know the value you are testing for ahead of runtime. Otherwise you could do:
也就是说，如果您不知道在运行之前要测试的值。否则你可以这样做：
alert( /John$/.test("blahJohn") );
回答by Sachin Shanbhag
Try this -
尝试这个 -
var reg = "/" + id + "$/";
var exists ="blahJohn".match(reg);
回答by lonesomeday
The nicer way to do this is to use RegExp.test:
更好的方法是使用RegExp.test：
(new RegExp(id + '$')).test('blahJohn'); // true
(new RegExp(id + '$')).test('blahJohnblah'); // false
Even nicer would be to build a simple function like this:
更好的是构建一个像这样的简单函数：
function strEndsWith (haystack, needle) {
return needle === haystack.substr(0 - needle.length);
}
strEndsWith('blahJohn', id); // true
strEndsWith('blahJohnblah', id); // false
回答by stephen mc
I like @lonesomeday 's solution, but Im fan of extending the String.prototype in these scenarios. Here's my adaptation of his solution
我喜欢 @lonesomeday 的解决方案，但我喜欢在这些场景中扩展 String.prototype。这是我对他的解决方案的改编
String.prototype.endsWith = function (needle) {
return needle === this.substr(0 - needle.length);
}
So can be checked with
所以可以检查
if(myStr.endsWith("test")) // Do awesome things here.
Tasty...
可口...
回答by Alexander Sobolev
Why using RegExp? Its expensive.
为什么使用正则表达式？它的价格昂贵。
function EndsWith( givenStr, subst )
{
var ln = givenStr.length;
var idx = ln-subst.length;
return ( giventStr.subst(idx)==subst );
}
Much easier and cost-effective, is it?
更容易和划算，是吗？
回答by Stewie Griffin
var id = new RegExp("John");
var exists ="blahJohn".match(id);
alert(exists);
try this
尝试这个
回答by Dudi
If you need it for replace function, consider this regExp:
如果您需要它来替换功能，请考虑这个正则表达式：
var eventStr = "Hello% World%";
eventStr = eventStr.replace(/[\%]$/, "").replace(/^[\%]/, ""); // replace eds with, and also start with %.
//output: eventStr = "Hello% World";
//输出： eventStr = "Hello% World";
回答by Alexander
var id = "John";
(new RegExp(`${id}$`)).test('blahJohn'); // true
(new RegExp(`${id}$`)).test('blahJohna'); // false
`${id}$` is a JavaScript Template stringswhich will be compiled to 'John$'.
`${id}$` 是一个 JavaScript模板字符串，它将被编译为 'John$'。
The $after John in RegExp stands for end of stringso the tested string must not have anything after id value (i.e. John) in order to pass the test.
$RegExp 中的after John 代表字符串的结尾，因此被测试的字符串在 id 值（即 John）之后必须没有任何内容才能通过测试。
new RegExp(`${id}$`) - will compile it to /John$/(so if id shouldn't be dynamic you can use just /John$/ instead of new RegExp(`${id}$`) )
new RegExp(`${id}$`) - 将其编译为/John$/（所以如果 id 不应该是动态的，你可以只使用 /John$/ 而不是 new RegExp(`${id}$`) ）
回答by Ben Ronan
Here is a string prototype function that utilizes regex. You can use it to check if any string object ends with a particular string value:
这是一个使用正则表达式的字符串原型函数。您可以使用它来检查任何字符串对象是否以特定字符串值结尾：
Prototype function:
原型功能：
String.prototype.endsWith = function (endString) {
if(this && this.length) {
result = new RegExp(endString + '$').test(this);
return result;
}
return false;
}
Example Usage:
示例用法：
var s1 = "My String";
s1.endsWith("ring"); // returns true;
s1.endsWith("deez"); //returns false;
