What is the correct way to write this javascript function?

Question

I'm trying to understand javascript and javascript functions. This function is used to change the look of a button.

function changeButton(){
    btn.style.backgroundColor = btn.style.backgroundColor == "black" ? "white" : "black";
    btn.style.color = btn.style.color == "white" ? "black" : "white";
    btn.innerHTML = btn.innerHTML == 'GOOD JOB' ? 'CLICK ME' : 'GOOD JOB';
}

It works just fine. But when I look at this function I see a lot of repetition. The basic structure seems to be element = element == value1 ? value2 : value1

So in my mind this should work:

function toggleValue(elem, val1, val2){
    elem = elem == val1 ? val2 : val1
}

function changeButton(){
    var x = btn.style.backgroundColor
    var y = btn.style.color
    var z = btn.innerHTML
    toggleValue(x, 'white', 'black')
    toggleValue(y, 'black', 'white')
    toggleValue(z, 'CLICK ME', 'GOOD JOB')
}

But it does not work and I don't understand why. Can someone tell me why this doesn't work? And is there a way to make it work?

A better way would be to use CSS and `classList.toggle` to turn the "active" class on and off. — georg, Jan 29 '18 at 13:14
`x.y = ...` modifies the property of an object. `x = ...` reassigns a local variable. — deceze, Jan 29 '18 at 13:15
`var x = btn.style.backgroundColor`, in this you are just copying a `value` which is there in the `backgroundColor` property. This will not act as a `reference`. — Bharadwaj, Jan 29 '18 at 13:16

score 4 · Accepted Answer · edited Apr 22 '18 at 21:01

It does not work, because you hand over a primitive value an not a reference to the property.

function toggleValue(elem, prop, val1, val2){
    elem[prop] = elem[prop] == val1 ? val2 : val1
}

function changeButton(){
    toggleValue(btn.style, 'backgroundColor', 'white', 'black')
    toggleValue(btn.style, 'color', 'black', 'white')
    toggleValue(btn, 'innerHTML', 'CLICK ME', 'GOOD JOB')
}

score 3 · Answer 2 · answered Jan 29 '18 at 13:15

Because you are passing the String which is immutable.

You can create one more argument - property.

function toggleValue(elem, prop, val1, val2){
    elem[prop] = elem[prop] == val1 ? val2 : val1
}

function changeButton(){
    var x = btn.style;
    var y = btn.style;
    var z = btn;
    toggleValue(x, "backgroundColor", 'white', 'black');
    toggleValue(y, "color", 'black', 'white');
    toggleValue(z, "innerHTML", 'CLICK ME', 'GOOD JOB');
}

score 1 · Answer 3 · answered Jan 29 '18 at 13:57

function toggleValue(elem, val1, val2, ButtonStyleType) {        
        elem = elem == val1 ? val2 : val1;
        if (ButtonStyleType == 'backgroundColor')
            btn.style.backgroundColor = elem;
        else if (ButtonStyleType == 'color')
            btn.style.color = elem;
        else if (ButtonStyleType == 'innerHtml')
            btn.innerHTML = elem;
    }
    function changeButton() {        
        var x = btn.style.backgroundColor;
        var y = btn.style.color;
        var z = btn.innerHTML;
        toggleValue(x, 'green', 'yellow', 'backgroundColor');
        toggleValue(y, 'black', 'Orange', 'color');
        toggleValue(z, 'Default', 'GOOD JOB', 'innerHtml');
    }

<button id="btn" style="background-color:green; color:black;">Default</button><br />
        <br />
        <a style="cursor:pointer;color:blue;" onclick="changeButton();">Click here to update button style</a>

score 0 · Answer 4 · answered Jan 29 '18 at 13:30

0

You have to understand the difference between pass by value and pass by reference to know more about that click here

answered Jan 29 '18 at 13:30

RaM PrabU

415
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16

What is the correct way to write this javascript function?

4 Answers4