javascript settimeout run immediately code example

Example 1: js after settimeout

function doHomeWork(subject, callback){
    setTimeout(callback,500);
    console.log("doing my homework:", subject)
}

doHomeWork("Maths", function(){console.log("finished my homework");});

Example 2: javascript this in settimeout

function func() {
  this.var = 5;
  
  this.changeVar = function() {
    setTimeout(() => { //Don't use function, use arrow function so 'this' refers to 'func' and not window
      this.var = 10;
    }, 1000);
  }
}

var a = new func();
a.changeVar();