javascript regex: string contains this, but not that

Question

I'm trying to put together a regex pattern that matches a string that does contain the word "front" and does NOT contain the word "square". I have can accomplish this individually, but am having trouble putting them together.

front=YES

 ^((?=front).)*$

square=NO

 ^((?!square).)*$

However, how to I combine these into as single regex expression?

Answer 1

You can use just a single negative lookahead for this:

/^(?!.*square).*front/

RegEx Demo

RegEx Details:

• ^ : Start
• (?!.*square) is negative lookahead to assert a failure if text square is present anywhere in input starting from the start position
• .*front will match front anywhere in input

Answer 2

You could use lookahead assertions to express the logical and:

The final pattern would look like that:

^(?=.*?front)(?!.*square)