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Change background color between red and green every second

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终归单人心
终归单人心 2020-12-19 16:10

I\'m trying to make a webpage change the background color every one second using JavaScript. I\'m using setTimeout but I can\'t figure out how to get my variabl

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  • 醉梦人生
    2020-12-19 16:43

    Your code is missing the closing </script> tag and other issues mentioned above.

    Find below a fix of your code that removes the global variable.

     <html> 
     <head> 
         <script type="text/javascript">
         function changecolors() {    
             var t = setInterval('change()',1000); 
         } 

         function change() {
             var color = document.body.style.background;

             if(color == "red") {
                 document.body.style.background = "green";
             } else {
                 document.body.style.background = "red";
             }
         } 
        </script>
     </head> 
     <body onload="javascript:changecolors()"> 
     </body> 
 </html>
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  • 别那么骄傲
    2020-12-19 16:46

    There are several problems here. I’ll just fix your code:

    var x;

function changecolors() {
    x = 1;
    setInterval(change, 1000);
}

function change() {
    if (x === 1) {
        color = "red";
        x = 2;
    } else {
        color = "green";
        x = 1;
    }

    document.body.style.background = color;
}

    Basically...

    • You need setInterval instead of setTimeout. setTimeout only executes once.
    • = assigns, even in an if statement. You need == (or better, ===).
    • You shouldn't pass a string to setTimeout or setInterval. Instead, pass a function.

    Another point of note: you shouldn’t use the on* attributes of HTML elements for event listeners, but especially not on <body>, since you can do this in JavaScript instead, and be unobtrusive:

    window.onload = changecolors;

    Of course, you could do it with fewer functions and no pollution of the global namespace.

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  • 天涯浪人
    2020-12-19 16:51

    x = 1; assigns x a value of 1, even in an if statement. Use x == 1 in if statements to keep the value of your variable unchanged.

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  • 一整个雨季
    2020-12-19 16:52

    For one thing, this:

    if (x = 1){

    Should be this:

    if(x == 1) {

    Your statement sets x to 1, rather than tests it to see if it's 1.

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