It's possible do an block-code when something happen? JAVASCRIPT [duplicate]

This question already has an answer here:

• Listening for variable changes in JavaScript or jQuery 15 answers

I was googling and i didn't see something like my query. So, it's like this, i want to do an block-code when a variable change to true like this.`

var query = false;
query = true;
(when query turns true) {
  (block-code)
}

via Pedro Pinto