JQuery function does operation when it receives date

Hello, I have a function in JQuery that receives a date parameter in the form Y-m-d, but when I get this data it does a subtraction math operation and returns the result. I took a look at the forum and did not find any similar question, could anyone help me?

function funcao(id_cliente,data) { 
   alert(data);
} 

Example: I sent the value 2018-09-18, it treats like 1991.