EN
TypeScript - escape special characters in regular expression pattern
3 points
In this short article, we would like to show how to escape special characters from patterns that we want to use with regular expressions in TypeScript.
Practical example:
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const SPECIAL_CHARACTERS_EXPRESSION: RegExp = /[.*+?^${}()\[\]\\|]/g;2
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// Escapes regular expression pattern special characters in the indicated string.4
//5
const escapePattern = (pattern: string): string => {6
return pattern.replace(SPECIAL_CHARACTERS_EXPRESSION, '\\$&');7
};8
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// Usage example:11
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const pattern: string = escapePattern('.*');13
const expression: RegExp = new RegExp(pattern, 'g');14
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const text: string = 'this is example text with .* and .* and .*';16
const result: string[] = text.match(expression);17
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console.log(pattern); // '\.\*'19
console.log(result); // ['.*', '.*', '.*']Output:
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\.\*2
[ '.*', '.*', '.*' ]Hint: the above approach is useful when we want to escape all special characters automatically.
We can escape special characters manually by using \ or \\ before them in patterns.
In strings, we should escape special characters using \\.
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const expression: RegExp = new RegExp('\\.\\*', 'g');2
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const text: string = 'this is example text with .* and .* and .*';4
const result: string[] = text.match(expression);5
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console.log(result); // ['.*', '.*', '.*']Output:
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['.*', '.*', '.*']
In syntax patterns, we should escape special characters using \.
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const expression: RegExp = /\.\*/g;2
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const text: string = 'this is example text with .* and .* and .*';4
const result: string[] = text.match(expression);5
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console.log(result); // ['.*', '.*', '.*']Output:
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[ '.*', '.*', '.*' ]
escapePattern() function is faster by about 2.5x than the replace-based version.
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// Escapes regular expression pattern special characters in the indicated string.2
//3
const escapePattern = (pattern: string): string => {4
let result = '';5
for (let i = 0; i < pattern.length; ++i) {6
const entry = pattern[i];7
switch (entry) {8
case '.':9
case '*':10
case '+':11
case '?':12
case '^':13
case '$':14
case '{':15
case '}':16
case '(':17
case ')':18
case '[':19
case ']':20
case '|':21
case '\\':22
result += '\\' + entry;23
break;24
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default:26
result += entry;27
break;28
}29
}30
return result;31
};32
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// Usage example:35
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const pattern: string = escapePattern('.*');37
const expression: RegExp = new RegExp(pattern, 'g');38
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const text: string = 'this is example text with .* and .* and .*';40
const result: string[] = text.match(expression);41
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console.log(pattern); // '\.\*'43
console.log(result); // ['.*', '.*', '.*']Output:
xxxxxxxxxx1
\.\*2
[ '.*', '.*', '.*' ]
escapePattern() function is faster by about 1.5x than the replace-based version.
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const SPECIAL_CHARACTERS: Record<string, number> = {'.': 1, '*': 1, '+': 1, '?': 1, '^': 1, '$': 1, '{': 1, '}': 1, '(': 1, ')': 1, '[': 1, ']': 1, '|': 1, '\\': 1};2
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// Escapes regular expression pattern special characters in the indicated string.4
//5
const escapePattern = (pattern: string): string => {6
let result = '';7
for (let i = 0; i < pattern.length; ++i) {8
const entry = pattern[i];9
result += SPECIAL_CHARACTERS[entry] ? '\\' + entry : entry;10
}11
return result;12
};13
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// Usage example:16
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const pattern: string = escapePattern('.*');18
const expression: RegExp = new RegExp(pattern, 'g');19
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const text: string = 'this is example text with .* and .* and .*';21
const result: string[] = text.match(expression);22
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console.log(pattern); // '\.\*'24
console.log(result); // ['.*', '.*', '.*']Output:
xxxxxxxxxx1
\.\*2
[ '.*', '.*', '.*' ]
