Problem with addEventListener

Hello, I need help. I have addEventListener and I need to change sing ( + to - , - to *, * to /, / to +). My addEventListener once it changes and that all. This is my code.

var labelSign1 = Ti.UI.createLabel({
    text: "+",
    left: "14%"
});
 
labelSign1.addEventListener("click", function(e){
    if(e.source.text = "+"){
        e.source.text = "-";
    }else if(e.source.text = "-"){
        e.source.text = "*";
    }else if(e.source.text = "*"){
        e.source.text = "/";
    }else if(e.source.text = "/"){
        e.source.text = "+";
    }
});