RegexpGarden

Garden Text Representation

let garden = "Rose\tRosemary\tRose\tRose\tPrimrose\t

Rose\tRosemary\tRose\tRose\tRosemary";

Code Editor
Log

123456

garden = garden

.replace(//gi, "Blackberry");

Lesson 32 / 42

Lesson task •

Replace with blackberry every rose that is followed directly by rose

Positive lookahead

(?=...)

/x(?=y)/ matches "x" only if it is directly followed by "y"

Useful for replacing when you need to conditionally replace some pattern1 witch is followed by another pattern2, and the pattern2 should not be replaced.

For the simple cases where you need to check if the string matches pattern1 followed by pattern2, you can simply write pattern2 after pattern1 in the regular expression - it would be more simple and performant solution with the same result:

1234

console.log(!!"foo42".match(/foo(?=\d*)/gi)) // true

console.log(!!"foo42".match(/foo\d*/gi)) // true

console.log("foo42".replace(/foo(?=\d*)/gi, "bar")) // bar42

console.log("foo42".replace(/foo\d*/gi, "bar")) // bar