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Regex Sticky Flag

Regular Expressions: Regex Sticky Flag

What does the regex flag ‘Y’ do in regular expressions?

View Answer:
Interview Response: The flag y allows us to perform the search at the given position in the source string. The flag y makes regexp.exec(str) search strictly at position lastIndex, not “starting from” it. There is a critical performance gain when using flag y.

Code Example:

let str = 'let varName = "value"';

let regexp = /\w+/y;

regexp.lastIndex = 3;
alert(regexp.exec(str)); // null (there's a space at position 3, not a word)

regexp.lastIndex = 4;
alert(regexp.exec(str)); // varName (word at position 4)