JavaScript函数默认参数-编程知识

JavaScript函数默认参数

首先我们写一个简单的预订功能；

'use strict';
const bookings = [];const createBooking = function (flightNum, numPassengers, price) {const booking = {flightNum,numPassengers,price,};console.log(booking);bookings.push(booking);
};createBooking('LH123');

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● 因为我们没有给后面两个参数传值，所有会显示undefined，当然我们可以给参数设置一个初始值；

'use strict';
const bookings = [];const createBooking = function (flightNum, numPassengers, price) {numPassengers = numPassengers || 1;price = price || 199;const booking = {flightNum,numPassengers,price,};console.log(booking);bookings.push(booking);
};createBooking('LH123');

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● 这种给参数默认值的方法是ES5提供的，但是这种太过于繁重和丑陋，在ES6中，我们可以直接使用这种方式

'use strict';
const bookings = [];const createBooking = function (flightNum, numPassengers = 1, price = 199) {const booking = {flightNum,numPassengers,price,};console.log(booking);bookings.push(booking);
};createBooking('LH123');

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● 当然，我们给函数传参的话，当然不会再是默认值了

'use strict';
const bookings = [];const createBooking = function (flightNum, numPassengers = 1, price = 199) {const booking = {flightNum,numPassengers,price,};console.log(booking);bookings.push(booking);
};createBooking('LH123');
createBooking('LH123', 3, 600);

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● 除此之外，默认的参数也可以随其他的参数而变动，如果价格按照人数来

确定
'use strict';
const bookings = [];const createBooking = function (flightNum,numPassengers = 1,price = 199 * numPassengers
) {const booking = {flightNum,numPassengers,price,};console.log(booking);bookings.push(booking);
};createBooking('LH123');
createBooking('LH123', 3);
createBooking('LH123', 5);

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● 如果我想跳过人数，给价格赋值，可以这样

'use strict';
const bookings = [];const createBooking = function (flightNum,numPassengers = 1,price = 199 * numPassengers
) {const booking = {flightNum,numPassengers,price,};console.log(booking);bookings.push(booking);
};createBooking('LH123');
createBooking('LH123', 3);
createBooking('LH123', 5);createBooking('LH123', undefined, 1000);