Javascript - When a string does not Match itself

Question

I have this Example 1:

myString = 'cdn.google.com/something.png';
console.log(myString.match(myString));

Everything works just fine, but when it comes to Example 2:

myString = 'cdn.google.com/something.png?231564';
console.log(myString.match(myString));

It returns the value of 'null'. I don't know what happened anymore.. I searched for the keywords 'a string does not Match itself' and found nothing. Can somebody help me? Thank you.

the `match` the first argument treat as regex(by parsing it)... in regex `?` has special meaning — Pranav C Balan, May 09 '17 at 10:13
Is there a way that I can make the match 'litteral'? Thank you — Tin Vịt TV, May 09 '17 at 10:14
For further information, you can check out some [documentation](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/match) on `match` — George, May 09 '17 at 10:15

Pranav C Balan · Accepted Answer · 2017-05-09T10:25:37.673

The String#match method would treat the argument as a regex(by parsing if not), where . and ? has special meaning.

. matches any character (except for line terminators)
? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed

So . wouldn't cause any problem since . can be used to match any character except line but ? would since it's using to match zero or one-time occurrence of any character.

For eg: .png?23 => matches .png23 or .pn23

From MDN docs :

If a non-RegExp object obj is passed, it is implicitly converted to a RegExp by using new RegExp(obj).

It's better to use String#indexOf instead which returns the index in the string if found or returns -1 if not found.

console.log(myString.indexOf(myString) > -1);

score 0 · Answer 2 · answered May 09 '17 at 10:15

0

match in Javascript compares a String against a RegEx. Luckily in your first example it works.

I guess you are looking for a method like localCompare.

Hope this helps!

answered May 09 '17 at 10:15

Stuti Rastogi

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Thank you very much. Is there a same method that can replace 'replace' method like this localCompare method? thank you :) – Tin Vịt TV May 09 '17 at 10:19
Thank you very much bro! – Tin Vịt TV May 09 '17 at 10:20
I am unfortunately not aware of such a method for replace. You can try `str.split(search_string).join(replace_string)`. That should replace all occurrences. – Stuti Rastogi May 09 '17 at 10:23

score 0 · Answer 3 · answered May 09 '17 at 10:23

match() search the string using a regular expression pattern.

So

var s = "My String";
s.match(/Regex Here/);

will try to match s for given regular expression .

In your example:-

myString = 'cdn.google.com/something.png'; // It will be treated as regex
console.log(myString.match(myString));

myString = 'cdn.google.com/something.png?231564';  // It will be treated as regex , result differ because of ? 
console.log(myString.match(myString));

score 0 · Answer 4 · edited May 23 '17 at 11:47

You can escape the argument to match, however if you do that you could just use == to compare the strings. This post contains a regex string escape function:

How to escape regular expression in javascript?

RegExp.quote = function(str) {
    return (str+'').replace(/[.?*+^$[\]\\(){}|-]/g, "\\$&");
};

It can be used like this:

myString = 'cdn.google.com/something.png?231564';
console.log(myString.match(RegExp.quote
(myString)));

If you want to match any number after the question mark, you could do it like this:

myString = 'cdn.google.com/something.png?';
console.log((myString+"18193819").match(RegExp.quote
(myString) + '\\d+'));

Javascript - When a string does not Match itself

4 Answers4