## 參數默認值 ``` function show(a, b = 'hello') { console.log(a, b); } ``` ## 參數解構函數 ``` function foo({name = 'jack', age = 20} = {}) { //注意,這里是等號 console.log(name, age); } //如果是調用的解構對象,一定要傳參,否則會報錯,或者像上面一樣, 等于一個空對象 foo({ name: 'milan', age: 50, }) ``` ## rest參數(剩余參數) ``` function foo(a,...rest) { console.log(a,rest) } foo(1,2,3,4) ``` 結果 ``` 1 (3)?[2, 3, 4] //把剩余的參數都放進了后面的數組中 ``` ## ...擴展運算符 ``` console.log(...[1,2,3]); ``` 結果,把一個數組拆散 ``` 1 2 3 ``` ``` function counter(a, b, c) { console.log(a + b + c); } counter(...[1, 2, 3]); ``` ### 合并數組 ``` var arr1 = [1, 2, 3]; var arr2 = [4, 5, 6]; var arr3 = [...arr1, ...arr2]; console.log(arr3); ```