方法一：
通過 lodash 比較簡單
安裝：npm i --save lodash
引入：import * as _ from 'lodash'
使用：
_.difference([1, 2, 3, 5], [3, 4, 5, 6]); // => [1, 2]
方法二：
let a = [1,2,3,5]
let b = [3,4,5,6]
let fn = () => fa.filter(item => !b.includes(item))
console.log('哈哈：', fn(a, b)) // [1,2]
方法三：
let a = [1,2,3]
let b = [3,4,5,6]
let result = []
arrA.forEach(item => {
if(a.includes(item) && !b.includes(item)) result.push(item)
})
console.log( result) // [1,2]
方法四：
let
a = [1, 2, 3];
let b = [3, 4, 5, 6];
let obj = {};
b.forEach(n => obj[n] = true);
let result = a.filter(n => !obj[n])
console.log( result) // [1,2]
方法五：
let a = [1, 2, 3];
let b = [3, 4, 5, 6];
let result = []
for (let i = 0; i < a.length; i++) {
if (b.indexOf(a[i]) == -1) {
result.push(a[i])
}
}
console.log( result) // [1,2]