how son hijack prevent by prefix some string

I shaw the following comment in spring json messageConverter

how does it works to prevent JSON hijack by prefix this prefix String ?

/** * Indicate whether the JSON output by this view should be prefixed with "{} &&". Default is false. * <p>Prefixing the JSON string in this manner is used to help prevent JSON Hijacking. * The prefix renders the string syntactically invalid as a script so that it cannot be hijacked. * This prefix does not affect the evaluation of JSON, but if JSON validation is performed on the * string, the prefix would need to be ignored. */