JavaScript/函数/练习
< JavaScript | 函数
主题：函数
1. 定义一个带一个参数的函数。该函数返回一个字符串，以“给定的参数是：”开头，以“. 好吗？”结尾。在两个字符串之间插入参数。
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"use strict";
// declare the function
function decorate(str) {
const ret = "The given argument is: " + str + ". Ok?";
return ret;
}
// call the function
let tmp = decorate("Francis");
alert(tmp);
tmp = decorate("Drake");
alert(tmp);
2. 扩展上一个函数以处理不同的数据类型，例如数字、对象等。在返回的字符串中显示数据类型。
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"use strict";
// declare the function
function decorate(param) {
let dataType = "";
let paramAsString = "";
switch (typeof param) {
case "object":
dataType = "object";
paramAsString = JSON.stringify(param);
break;
case "string":
dataType = "string";
paramAsString = param;
break;
// next case ...
default:
dataType = "???";
paramAsString = param;
}
const ret = "The given argument is: " + paramAsString + " It's data type is: " + dataType + ". Ok?";
return ret;
}
// call the function
let tmp = decorate("Francis");
alert(tmp);
tmp = decorate(42); // a number
alert(tmp);
tmp = decorate({temperature: "25° C"}); // an object
alert(tmp);
3. 定义一个接受两个参数的函数。该函数返回两个参数的平均值。
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"use strict";
// declare the function
function average(num1, num2) {
return (num1 + num2) / 2;
}
// call the function
alert(average(2, 4));
alert(average(2.4, 2.6));
4. 使用箭头函数定义第一个练习的函数。
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"use strict";
// declare the function and reverence it by a variable
const decorate = (str) => "The given argument is: " + str + ". Ok?";
// call the function
let tmp = decorate("Francis");
alert(tmp);
// or, even more compact:
tmp = (str => "The given argument is: " + str + ". Ok?")("Drake");
alert(tmp);
5. 定义一个函数，该函数接受一个数字数组作为参数。该函数返回数组的长度、最小元素、最大元素和所有元素的平均值。
由于函数只能返回单个元素，因此所有计算的值必须打包到一个数组（或对象）中。该数组是返回值。
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"use strict";
function checkArray(arr) {
// local variables
let min = arr[0];
let max = arr[0];
let sum = 0;
// a 'forEach' construct with an anonymous function
arr.forEach((elem) => {
if (elem < min) { min = elem };
if (elem > max) { max = elem };
sum = sum + elem;
});
// the length and average can be computed here
// 'pack' everything in an array: []
return [arr.length, min, max, sum / arr.length];
}
// the return value is an array
let ret = checkArray([2, 4, 6, 8]);
alert(ret);
// or:
let [length, min, max, avg] = checkArray([2, 4, 6, 8, 10]);
alert ("Length: " + length + ", Min: " + min + ", Max: " + max + ", Average: " + avg);
6. 定义一个描述汽车的函数。它接受四个参数：生产商、型号、马力、颜色。前两个是必需的；后两个是可选的。为后两个参数定义默认值，例如“未知”。
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"use strict";
// supply default values if they are not given
function showCar(producer, model, horsepower = "unknown", color = "unknown") {
let ret = "";
if (!producer || !model) {
return "Producer and model must be specified";
}
ret = "My car is produced by " + producer;
ret += ". The model is: " + model;
ret += ". The horsepower is: " + horsepower;
ret += ". The color is: " + color;
return ret;
}
alert(showCar("Ford", "Mustang", 300, "blue"));
alert(showCar("Ford", "Mustang GT", 350));