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JavaScript - flag y meaning in regex (sticky flag)
5 points
In this short article, we would like to explain flag y meaning in regular expression in JavaScript.
Qucik solution:
When the
y(sticky) flag is used,RegExpclass matches pattern only whenlastIndexproperty indicates strat of expected sub-string directly.
Practical example:
xxxxxxxxxx1
// indexes: 0 32
// | |3
// v v4
const string = 'abcd';5
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// pattern7
// ||8
// vv9
const expression = /bc/y; // OR: new RegExp('bc', 'y');10
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expression.lastIndex = 0;12
console.log(expression.test(string)); // false13
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expression.lastIndex = 1;15
console.log(expression.test(string)); // true // OR: expression.exec(text) // ['bc']16
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expression.lastIndex = 2;18
console.log(expression.test(string)); // false19
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expression.lastIndex = 3;21
console.log(expression.test(string)); // false
