将变量另存为JavaScript中的cookie？

Question

I have a function that displays or hides a menu, but if I refresh the variable is reset to 0 . What I want is to keep the variable value it's currently at in between page refreshes, which I guess you do with cookies? However I don't know how.

visible = 0; // Want this variable to keep it's value

function menu(id)
{
    if(visible == 0) {
        document.getElementById(id).style.display = "block";
        visible = 1;
    }
    else {
    document.getElementById(id).style.display = "none";
    visible = 0;
    }
}

Answer 1

Managing cookies in JavaScript is ugly unless you use a framework. The benefit of using a cookie is that you don't have to worry about compatibility with old browsers. However, if you don't care about old browsers then you can use HTML5 Local Storage (aka Web Storage), which allows you to persist basic key/value pairs of strings.

HTML5 Local Storage (Web Storage) example

Demo: http://jsfiddle.net/9zsH4/

In the demo, try toggling the menu then refresh the page to see its state be persisted.

function getVisible(){
    var value = localStorage.getItem('visible');
    return value == '1';
}

function setVisible(visible){
    localStorage.setItem('visible', (visible ? '1' : '0'));
}

function menu(id)
{
    if(!getVisible()) {
        document.getElementById(id).style.display = "block";
        setVisible(true);
    } else {
        document.getElementById(id).style.display = "none";
        setVisible(false);
    }
}

• Web Storage documentation on w3.org

---

Cookie Example

This example uses the minimal framework from MDN here , so be sure to include the docCookies framework.

function getVisible(){
    var value = docCookies.getItem('visible');
    return value == '1';
}

function setVisible(visible){
    docCookies.setItem('visible', (visible ? '1' : '0'), new Date(2015, 5, 12));
}

function menu(id)
{
    if(!getVisible()) {
        document.getElementById(id).style.display = "block";
        setVisible(true);
    } else {
        document.getElementById(id).style.display = "none";
        setVisible(false);
    }
}

Edit: to explain this line:

localStorage.setItem('visible', (visible ? '1' : '0'));

Here I'm using the ternary operator. It's just a shorthand if/else, so it's the same as doing:

if(visible){
    localStorage.setItem('visible', '1');
} else {
    localStorage.setItem('visible', '0');
}

Another example: get a human Yes/No representation of a boolean.

var something = true;
var humanText = something ? 'Yes' : 'No';
console.log(humanText); // Yes

var something = false;
var humanText = something ? 'Yes' : 'No';
console.log(humanText); // No

As you can see, the first part is evaluated and if the result equates to true , the question mark part is used, else the colon part is used.

See this question for more examples.

Answer 2

Cookies are not appropriate for this, as they will be sent to the server with every request.

Instead, use storage. Keep your current code and replace visible with localStorage.visible . This will allow the variable to persist across pageloads.

Additionally, you will need to add if( localStorage.visible) document.getElementById('yourID').style.display = 'block'; independently of the menu function, so that when the page is loaded then the initial state is applied.