javascript

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javascript関連

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概要

  • 同じことをするのにたくさんのやり方がある

具体例

数値を特定小数点でroundする

> parseFloat("1.23456").toFixed(2);
'1.23'

arrayに要素が含まれているかどうか

> const fruits = ["Banana", "Orange", "Apple", "Mango"];
undefined
> fruits.includes("Mango");
true
> fruits.includes("XXX");
false

arrayのpopとshift

shift

> const fruits = ["Banana", "Orange", "Apple", "Mango"];
undefined
> fruits.shift();
'Banana'
> fruits
[ 'Orange', 'Apple', 'Mango' ]

pop

> const fruits = ["Banana", "Orange", "Apple", "Mango"];
undefined
> fruits.pop()
'Mango'
> fruits
[ 'Banana', 'Orange', 'Apple' ]

固定サイズのarrayを作成する

一次元のarray

>  let array = Array(3).fill()
undefined
> array
[ undefined, undefined, undefined ]

二次元のarray

> let array = Array(5).fill().map(() => Array(3));
undefined
> array
[
  [ <3 empty items> ],
  [ <3 empty items> ],
  [ <3 empty items> ],
  [ <3 empty items> ],
  [ <3 empty items> ]
]

arrayの要素をスワップ

> let list = ["a", "b", "c"]
undefined
> list
[ 'a', 'b', 'c' ]
> [list[0], list[2]]
[ 'a', 'c' ]
> [list[0], list[2]] = [list[2], list[0]]
[ 'c', 'a' ]
> list
[ 'c', 'b', 'a' ]
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