DOM basics (V)

Date Object Date ()

• In the computer era: 1970.01.01

• Each object created out of date records to that moment of time

• doc

• getTime () can be calculated time interval (ms)

  var start = new Date().getTime();
  for (var i = 0; i < 100000000; i ++>) {}
  var end = new Date().getTime();
  console.log(end - start);

• For example scenarios

  • Limit spike shopping

  • Alarm Clock

  • Any need to obtain the time difference scene

Timer

• The method of the global object window setInterval (), setTimeout (), clearInterval (), clearTimeout () is, inside this point window function

• setInterval and setTimeout first frame is not executed

• Once the timer into effect until canceled timer, Timeout._idleTimeout (ie, the time interval callback function is executed) can not be changed dynamically

  var time = 1000;
  timer = setInterval(()=> {
    console.log(1);
  }, time);
  time = 2000;
  // 依然每隔一秒打印一次1

• In fact, the timer is not precise in terms of timing

var start = new Date().getTime();
setInterval(()=>{
  var end = new Date().getTime();
  console.log(end - start);
  start = end;
}, 1000);

• The Executive, print the results in 1000 or 1000, is not accurate

• Queue considerations executed from js, every 1000ms just a callback function into the execution queue, and can not guarantee timely implementation

• Timer data structure based on a red-black tree, so there is less than 1000ms callback function is executed

• Retrieved from "high-performance JavaScript" && "you do not know JS"

• setTimeout scenarios distance

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