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. .

JavaScript- , , .

arr.forEach(func) func forEach .
setTimeout(func) func .
.

JavaScript.

. .

this

, "this", this. this, .

, :

let group = {
  title: " ",
  students: ["", "", ""],

  showList() {
    this.students.forEach(
      student => alert(this.title + ': ' + student)
    );
  }
};

group.showList();

forEach , this.title , showList, group.title.

, :

let group = {
  title: " ",
  students: ["", "", ""],

  showList() {
    this.students.forEach(function(student) {
      // Error: Cannot read property 'title' of undefined
      alert(this.title + ': ' + student);
    });
  }
};

group.showList();

, forEach this=undefined , undefined.title.

, this.

this : . new.

=> , .bind(this) :

.bind(this) .
=> . this. this , : .

arguments

arguments.

, this arguments.

, defer(f, ms) , ms :

function defer(f, ms) {
  return function() {
    setTimeout(() => f.apply(this, arguments), ms);
  };
}

function sayHi(who) {
  alert(', ' + who);
}

let sayHiDeferred = defer(sayHi, 2000);
sayHiDeferred(""); // ", "  2

          function defer(f, ms) {
  return function(...args) {
    let ctx = this;
    setTimeout(function() {
      return f.apply(ctx, args);
    }, ms);
  };
}
        

args and ctx, setTimeout .

this
arguments
new
super, .

, , , . .