Lookahead and Lookbehind assertions, also known as Lookaround assertions are basically special type of non-matching group. It is a condition that must be satisfied in order to return the match to an expression. These are of zero-length i.e. the match is grouped and there is no change in the position of regex pointer. Positive Lookahead Assertion : Syntax : /(?=regex-expression)/ Example : Let's say if we want to capture the word " background " only if it is in a camel case word " backgroundColor". /background(?=Color)/ => This will match "background" as a group for text "backgroundColor" and no match for "backgroundText" Negative Lookahead Assertion : Syntax : /(?!regex-expression)/ Example : Let's say if we want to capture the word " background " only if it is NOT in a camel case word " backgroundColor". /background(?!Color)/ => This will match "bac