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通常関数とアロー関数の違い

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#通常関数とアロー関数の記述
以下,二つの関数の記述法である.

//function 
function f(x) {
  return x + 1;
}

//arrow function 
const f = (x) => x + 1;

#通常関数とアロー関数とでは参照するthisが異なる
JavaScriptでは,関数もconstructor同様にthisのオブジェクトを持つことができる.
このthisオブジェクトの参照先が通常関数とアロー関数とで異なる.

  • 通常関数:宣言元のオブジェクト
//////通常関数のthis//////
function test1 {
  this.param = 'test1' //JavaScriptでは関数の中に関数を持つことも可能

  function printParam () {
    console.log( this.param )
  }

  let object1 {
    param: 'object1',
    func: printParam(),
  }

  let object2 {
    param: 'object2',
    func: printParam(),
  }

  object1.func()
  object2.func()
}

test1()
出力
object1
object2
  • アロー関数:宣言時のスコープを持つオブジェクト
///////アロー関数///////
function test2 {
  this.param = 'test2' //JavaScriptでは関数の中に関数を持つことも可能

  function printParam () {
    console.log( this.param )
  }

  let object3 {
    param: 'object3',
    func: printParam(),
  }

  let object4 {
    param: 'object4',
    func: printParam(),
  }

  object3.func()
  object4.func()
}

test2()
出力
test2
test2
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