易忘js记录

map

Array.map 数组方法 数组内子元素执行括号内方法 原数组不改变。
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//ES5（数组*2）
var numbers = [1, 4, 9];
var doubles = numbers.map(function(num) {
  return num * 2;
});
//[2, 8, 18]

// ES6（数组平方）
let numbers = [1, 5, 10, 15];
let doubles = numbers.map( x => x ** 2);

// doubles is now [1, 25, 100, 225]
// numbers is still [1, 5, 10, 15]

//（数组/2）
const numbers = [2, 4, 8, 10];
let halves = numbers.map(x => x / 2);

//（数组平方根）
let numbers = [1, 4, 9];
let roots = numbers.map(Math.sqrt);
// roots is now [1, 2, 3]
// numbers is still [1, 4, 9]

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