实现函数的闭包和自调用

Question

In this, I am trying to assign the start time in the beginning and when I will click on the page it should return me the time spent but I am getting 0 always. I am not understanding that where I might have gone. Need your help.

     var timeSpent = (function(){
        var time    = new Date();
        var timeRun = false,
            startTime = time.getTime();

        return function(){ // call this function by timeSpent()(); 
            return time.getTime() - startTime;
        }
    })();

    addEventListener("click", function(){
        console.log(timeSpent());
    })

Answer 1

You need to calculate the present time inside the inner function

 var timeSpent = (function(){ var time = new Date(); var timeRun = false, startTime = time.getTime(); return function(){ // call this function by timeSpent()(); return (new Date()).getTime() - startTime; } })(); addEventListener("click", function(){ console.log(timeSpent()); }) 

Answer 2

time is a date. Every time you call getTime() on it, you will get the same value.

So startTime and time.getTime() will always be the same.

You need to replace time.getTime() inside the returned function with something which will get the current time. (new Date()).getTime()

 var timeSpent = (function() { var time = new Date(); var timeRun = false, startTime = time.getTime(); return function() { // call this function by timeSpent()(); return (new Date()).getTime() - startTime; } })(); addEventListener("click", function() { console.log(timeSpent()); }) 

Answer 3

Your function timeSpent() is evaluated as (you can check it by logging the function in console)

return time.getTime() - startTime;

As, startTime = time.getTime() initially. Therefore, the above return statement will evaluted to 0. In order to get the current time, you will have to call new Date().getTime()

 var timeSpent = (function(){ var time = new Date(); var timeRun = false, startTime = time.getTime(); return function(){ // call this function by timeSpent()(); return new Date().getTime() - startTime; } })(); addEventListener("click", function(){ console.log(timeSpent()); })