I want to build a palindrome checker in javascript. All non-letter characters should be removed, so that a phrase like "A man, a plan, a canal. Panama" can also be a palindrome.
function reverse(str) {
return str.split("").reverse().join("");
}
function palindrome(str) {
str = str.replace(/[^a-zA-Z]+/,"").toLowerCase();
if(str == reverse(str)) {
return true;
}
else {
return false;
}
}
Now, where is the mistake in the above lines?
The code works on some examples. But for instance "A man, a plan, a canal. Panama" and "never odd or even" return false, meaning somewhere has to be a mistake.
You need to provide the global match flag to your regex:
/[^a-zA-Z]+/g
^
This is a common misconception. The replace() method does not replace all instances of what you want to replace in a string. It simply replaces the first instance and stops. If you refactor your regEx like this:
function reverse(str) {
return str.split("").reverse().join("");
}
function palindrome(str) {
var find = "[^a-zA-Z]";
var regEx = new RegExp(find, 'g');
str = str.replace(regEx,"").toLowerCase();
if(str == reverse(str)) {
return true;
}
else {
return false;
}
}
That will work.
From the example given, it seems to me that the code doesn't work for spaces in between the letters. (There may be other scenarios as well)
I have changed this line :
str = str.replace(/[^a-zA-Z]+/,"").toLowerCase();
To this :
str = str.toLowerCase().replace(/[^a-z]/g,"");
change this line:
str = str.replace(/[^a-zA-Z]+/,"").toLowerCase();
to this:
str = str.toLowerCase().replace(/[^a-z0123456789]+/g,"");
This regex should work for your code.
/[^1-9a-zA-Z]+/g
来源:https://stackoverflow.com/questions/32395229/palindrome-checker-in-javascript-dont-know-how-to-debug