如何通过引用将属性传递给javascript函数？

Question

I want to manipulate some attributes of my page elements in a java script function , take a look at this example and maybe you find a solution to do this.

function doubleup(attr){
attr*=2;
}
doubleup(myDIV.style.zIndex);
doubleup(myDIV.style.opacity);

Answer 1

In short, you don't. You can't pass primitive values by reference. You can do that with non-primitive values, though, as they're always passed as reference. Example:

function doubleup(object, property) {
    object[propety] *= 2;
}
doubleup(myDiv.style, "zIndex");
doubleup(myDiv.style, "opacity");

Primitive data types are strings, numbers, booleans and, recently, Symbol s

Answer 2

You only pass the value of this attribute to the function, so you don't change the style element, you only change the value, can do it in this way:

function doubleup(attr){
    return attr*=2;
}

myDIV.style.opacity = doubleup(myDIV.style.opacity);
myDIV.style.zIndex = doubleup(myDIV.style.zIndex);

By the way, you have to use zIndex instead of z-index to manipulate this value.

Another possible solution is:

function doubleup(el){
    el.style.opacity*=2;
}
function doubleupZIndex(el){
    el.style.zIndex*=2;
}

doubleupOpacity(myDIV);
doubleupZIndex(myDIV);