feat(es6): 新增剩余参数

Author: coderfocus

src/residual-parameters.js

@@ -0,0 +1,101 @@
+//++++++++++++++++++++++++++++++++++++++++++++++++
+//函数参数的默认值
+function powerOf(base,exponent = 2) {
+    return Math.pow(base,exponent)
+}
+
+console.log(powerOf(2));
+console.log(powerOf(2, undefined));
+console.log(powerOf(2, 3));
+
+var double = (value = 0) => value * 2
+console.log(double());
+console.log(double(2));
+
+//对象参数默认值
+// var defaultOption = {
+//     brand: 'volvo',
+//     make: 2019
+// }
+// function carFactory(option = defaultOption) {
+//     console.log(option.brand);
+//     console.log(option.make);
+// }
+// carFactory()
+// //volvo
+// //2019
+//
+// //如果传入一个对象参数，则所有的默认值都会失效
+// carFactory({})
+// // undefined
+// // undefined
+//
+// carFactory({make: 2010})
+// // undefined
+// // 2010
+
+//与提供一个默认参数相比，更好的办法是使用解构，并在解构模式中为每一个属性指定默认值
+function carFactory({brand = 'volvo',make = 2019}) {
+    console.log(brand);
+    console.log(make);
+}
+
+// carFactory({})
+// // volvo
+// // 2019
+//
+// carFactory({make: 2010})
+// // volvo
+// // 2010
+//
+// carFactory()
+// //Exception
+
+
+// 添加一个空对象作为默认值可避免该问题，因为解构空对象时已经提供了默认值
+function carFactory({brand = 'volvo',make = 2019} = {}) {
+    console.log(brand);
+    console.log(make);
+}
+
+carFactory()
+// volvo
+// 2019
+
+//只想在某个函数中提取对象的某些属性作为参数，可以通过解构提前显式地引用这些属性
+var getCarProductModel = ({brand,make,model} = {})=>({
+    sku: brand + ':' + make + ':' + model,
+    brand,
+    make,
+    model
+})
+
+var car = {
+    brand: 'volvo',
+    make: 2019,
+    // model: '201',
+    price: 280000,
+    color: 'red'
+}
+console.log(getCarProductModel(car));
+console.log(getCarProductModel({}));
+console.log(getCarProductModel());
+
+//++++++++++++++++++++++++++++++++++++++++++++++++++++++
+//剩余参数
+//在函数的最后一个参数前添加...可以将该参数转变为一个特殊的剩余参数。
+//当剩余参数是函数中的唯一参数时，它会获取所有传入函数的参数
+// function join(...list) {
+//     return list.join(',')
+// }
+// console.log(join('first', 'second', 'third'));
+
+// var join = (...list) => list.join(',')
+// console.log(join('first', 'second', 'third'));
+
+//剩余参数前面的参数不会包含在 list 参数中
+function join(separator,...list) {
+    return list.join(separator)
+}
+
+console.log(join(';', 'first', 'second', 'third'));