时间功能不起作用

因此，让我们从头开始，因为我将能够以此方式解释更多的事情。

首先，我们需要节省用户到达页面的时间。我们可以通过在页面加载后保存日期来做到这一点。

// The variable is outside because we need every function to
// be able to access it (like a global variable)
var userArrived;

// The function to initialize the counter
function initCounter(){
    // Get the date when the user arrived
    // here we do not use `var` because the variable exists
    userArrived = new Date().getTime(); // This returns the date in milliseconds
}

// Wait the page to load    
window.addEventListener('load', function(){
    // Initialize the counter
    initCounter();
}, false);

现在我们需要一个函数来给我们带来不同

function getCounterValue(){
    // Calculate difference
    var value = new Date().getTime() - userArrived;
    // This variable now have the time the user
    // is on the page in milliseconds

    // Now we need to return the value to the caller
    return value;
}

现在我们可以获得毫秒，我们需要一个函数将其解析为人类可读的格式。

function parseMs2Sec(ms){
    // We calculate seconds using seconds = milliseconds / 1000
    // but we round it so that we don't have decimals
    var sec = Math.round(ms/1000);
    // Now we need to return the value to the caller
    return sec;
}

现在唯一要做的就是每1秒（或更长时间）更新一次我们需要的任何视觉元素。

// Save the element on a variable for easy access
var timeSpent = document.forms[0].timespent;

// Update the screen with the latest time
function updateScreeenCounter(){
    // Get the time the user is in the page
    var ms = getCounterValue();
    // Convert it to seconds
    var sec = parseMs2Sec(ms);

    // Display it in the page
    timeSpent.value = sec + " sec."; 
}

// Every 1000 milliseconds
setInterval(function(){
    // Run function
    updateScreeenCounter();
}, 1000);
// But this last code (with the interval)
// needs to run after the counter was initialized
// so we should put it inside the onload event we created.

这是演示中的孔代码：

    //
    // The variable is outside because we need every function to
    // be able to access it (like a global variable)
    var userArrived;

    // The function to initialize the counter
    function initCounter(){
        // Get the date when the user arrived
        // here we do not use `var` because the variable exists
        userArrived = new Date().getTime(); // This returns the date in milliseconds
    }

    // Gives back the time since the user arrived on page (in ms)
    function getCounterValue(){
        // Calculate difference
        var value = new Date().getTime() - userArrived;
        // This variable now have the time the user
        // is on the page in milliseconds
        
        // Now we need to return the value to the caller
        return value;
    }

    // Converts the given ms in the closest seconds
    function parseMs2Sec(ms){
        // We calculate seconds using seconds = milliseconds / 1000
        // but we round it so that we don't have decimals
        var sec = Math.round(ms/1000);
        // Now we need to return the value to the caller
        return sec;
    }

    // Update the screen with the latest time
    function updateScreeenCounter(){
        // Get the time the user is in the page
        var ms = getCounterValue();
        // Convert it to seconds
        var sec = parseMs2Sec(ms);
        
        // Display it in the page
        document.forms[0].timespent.value = sec + " sec."; 
    }

    // Wait the page to load    
    window.addEventListener('load', function(){
        // Initialize the counter
        initCounter();
        // Every 1000 milliseconds
	    setInterval(function(){
	        // Run function
	        updateScreeenCounter();
	    }, 1000);
    }, false);

<form>
    <input name="timespent" value="Loading ..."/>
</form>

其他一些技巧：

1. 在这里再次阅读Javascript教程w3schools
2. 在此处阅读Chrome DevTools指南DevTools（Firefox和Opera也具有相同的功能）

~~~编辑~~~

我忘了提到setInterval在这种情况下使用它会更好，因为它setTimeout在慢速计算机中比递归更准确。