在 JavaScript 中使用 setInterval 在特定时间执行代码块

Question

I want to execute a block of code in a certain time. in order to do that I write a function called get_current which get the current time and by using setInterval and check the time in short interval, compare it to my desired time. If that condition is satisfied I execute a console.log() .

I have tested the code below and got sure that the checkStart() is executed in the inteval which is defined in the code but unfortunately that if condition is never satisfied. Does anybody have any idea why?

var dateString;


function get_current(){

var mydate = new Date();
var mili_real = mydate.getMilliseconds();
var hour_real=mydate.getHours();
var minute_real=mydate.getMinutes();
var second_real=mydate.getSeconds();
     if(minute_real<10)minute_real="0"+minute_real;

     if(hour_real==0)hour_real="12";

     if(second_real<10) second_real="0"+second_real;
     if(mili_real<10)mili_real="00"+mili_real;
     else if(mili_real<100) mili_real="0"+mili_real;

     dateString=hour_real+""+minute_real+""+second_real+""+mili_real;
}

setInterval(checkStart,1);

function checkStart(){
    get_current();
    if(dateString==18581600){
    console.log("It's time to start");  
    }
}

Answer 1

Trying to hit an exact time with 1 millisecond accuracy will not work. Change:

dateString==18581600

to:

dateString >= 18581600

Also, running setInterval with a 1 millisecond delay is not supported. 4ms is the minimum, but it can be longer.

When in doubt, consult the MDN reference for setInterval() :

[T]he browser will automatically enforce a 4 ms minimum value for the interval.

Browsers may enforce even more stringent minimum values for the interval under some circumstances, although these should not be common. Note also that the actual amount of time that elapses between calls to the callback may be longer than the given delay;