Regex is accepting words with symbols - Artificial Intelligence

YashwardhanPauranik
February 13, 2020
74 views
0 votes
2 Answers

I have a situation where I need to test the string if it contains a particular word or letter using the Javascript Regex.

Sample strings would be:

// In the first 3 strings, I need "C" letter to be checked in the string
C is language is required.     
We need a C language dev.
Looking for a dev who knows C!

// Keyword is Artificial Intelligence
We need looking for someone who knows Artificial Intelligence.

For checking the above I have created a Regex.

['C', 'Artificial Intelligence', 'D', 'Angular', 'JS'].forEach((item) => {
 const baseRex = /[!,.?": ]?/g;
 const finalRex = new RegExp(baseRex.source + item + baseRex.source); // /[!,.?": ]<C/D/Angular...>[!,.?": ]/

// Say checking for first iteration only. So let consider 'C'.
 console.log(finalRex.test('C is required')); // true
 console.log(finalRex.test('Looking for a dev who knows C!')); // true
 console.log(finalRex.test('We need a C language dev.')); // true
 console.log(finalRex.test('Computer needed')); // Also returns true | Which is wrong!

});

I won’t want the words contains the letter C also get a count.

Tags: javascript regex

Answers

- Sweeper
- February 13, 2020 at 7:56 am
- 0 votes
0
The regex after the concatenation with the baseRex is:
```
[!,.?": ]?C[!,.?": ]?
```
Notice that [!,.?": ]? can match 0 or 1 characters. In Computer, both subpatterns of [!,.?": ]? matches 0 characters, and C matches C, causing the whole regex to match.

Presumably, you added ? there so that it works at the start and end of the string, where there are no characters to be matched. However, you should instead use ^ and $ for the start and end instead. Your whole regex should be:
```
(?:[!,.?": ]|^)C(?:[!,.?": ]|$)
```
You can also replace the character class with W, which means [^0-9a-zA-Z_].

In fact, you don’t actually need to do all of this! There is a useful 0-width matcher called “word-boundary” b, which seems to be exactly the thing you want here. Your base regex can just be:
```
b
```
It only matches the boundary between a w and a W or between a W and a w.
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- crifan
- February 13, 2020 at 9:32 am
- 0 votes
0
for C

input:
```
C is language is required.     
We need a C language dev.
Looking for a dev who knows C!
Computer needed
invalidC should not match
```
- js regex: (?<!w)C(?!w)
- match result:
  - Chrome:
  - Safari: not support look behind
extended to both C or Artificial Intelligence

input:
```
C is language is required.     
We need a C language dev.
Looking for a dev who knows C!
Computer needed
invalidC should not match
We need looking for someone who knows Artificial Intelligence.
not matchArtificial Intelligence
```
- regex: (?<!w)((C)|(Artificial Intelligence))(?!w)
- match result:
  - Chrome:
Note

for more about look ahead and look behind, can refer my summary:
- one picture
- view online: 正则表达式详解：look ahead和look behind
and my (Chinese) tutorial: 环视断言 · 应用广泛的超强搜索：正则表达式

and even all regex: 一图让你看懂和记住所有正则表达式规则
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