JS基础第二课（函数、对象篇）

<script>
        function get() {
            console.log(1234);
        }
        get()
</script>

<script>
        var post = function() {
            console.log(123);
        }
        post()
</script>

<script>
        var post = function(a) {//这里的a是形参
            console.log(a);//运行函数结果输出10
        }
        post(10)//这里的10是实参
</script>

<script>
        var post = function(a) {//这里的a是形参
            console.log(a);//运行函数结果，还是输出10
        }
        post(10,23)//这里的10，23是两个实参
</script>

<script>
        var post = function(a,b) {//这里的a是形参
            console.log(a);//运行函数结果输出10
            console.log(b);//运行函数结果输出undefined
        }
        post(10)//这里的10是实参
</script>

<script>
        (function(a) {
            console.log('执行',a);
        })(10)
</script>

<script>
        (function(a){
            console.log('执行',a);
        }(20))
</script>

<script>
        var a = 10
        function test() {
            var b = 20
            console.log(a);//10
            console.log(b);//20
        }
        test()
        console.log(b);//b is not defined
</script>

<script>
        console.log(a);//不报错，只是输出为undefined
        var a=10
        function test() {
            console.log(b);//不报错，只是输出为undefined
            var b = 10
        }
        test()
        console.log(c);//报错c is not defined
</script>

<script>
        var str={//多个属性之间用逗号,隔开
            name:'小明',//属性和方法都是键值对
            age:18,
            sex:'男',
            hoppy:['学习','比赛'],
            say:function(){//方法后面跟的是匿名函数（不设置函数名）
                console.log('写文章啦');
                return '写到不能停'
            }
        }
        console.log(str);
        console.log(str.name);
        console.log(str['age']);
        console.log(str.hoppy);
        str.say();//直接调用方法，输出'写文章'
        console.log(str.say());//打印输出'写文章'、'写个不停'
</script>

<script>
        var user = new Object()
        user.name='小红'
        user.age=18
        console.log(user);
</script>

<script>
        function Person(name1,age1,sex1) {
            this.name = name1
            this.age = age1
            this.sex = sex1
        }
        var p1 = new Person("小红",10,'女')
        console.log(p1);
</script>

<script>
        function Person(name1,age1,sex1) {
            this.name = name1
            this.age = age1
            this.sex = sex1
        }
        var p1 = new Person("小红",10,'女')
        // console.log(p1);
        for(item in p1){
            console.log(item);
            console.log(p1[item]);
        }
</script>

<script>
        function name() {
            var str ='Hello world!';
            console.log(str.charAt(4));
            console.log(str.indexOf('l'));
            console.log(str.lastIndexOf('o'));
            console.log(str.includes('lo'));
            console.log(str.replace('llo','ok'));
            newstr = str.slice(2,6);
            console.log(newstr);
            newstr2 = str.split(3,8);
            console.log(newstr2);
            newstr3 = str.substr(2,4);
            console.log(newstr3);
            newstr4 = str.substring(5,9);
            console.log(newstr4);
        }
        name()
</script>

<script>
        var date = new Date()
        console.log(date.getFullYear());
        console.log(date.getMonth()+1);
        console.log(date.getDate());
        console.log(date.getDay());
        console.log(date.getHours());
        console.log(date.getMinutes());
        console.log(date.getSeconds());
        console.log(date.getTime());
</script>

<script>
        var arr = [1, 2, 3, 4, 5, 6];
        arr.push(7);
        console.log(arr);
        arr.pop();
        console.log(arr);
        console.log(arr.indexOf(2));
        console.log(arr.lastIndexOf(1));
        arr.forEach(function (item) {
            console.log(item);
        });
        console.log(arr.includes(2));
        console.log(arr.slice(1, 4));
</script>

<script>
        console.log(Math.PI);
        console.log(Math.abs(-123));
        console.log(Math.floor(3.14));
        console.log(Math.ceil(3.14));
        console.log(Math.round(3.14));
        console.log(Math.max(1,2,3,4,5));
        console.log(Math.min(1,2,3,4,5));
        console.log(Math.random());
</script>

<script>
        //1、求数组[1,23,54,121,33,4]所有元素的和以及平均值
        var arr1 = [1, 23, 54, 121, 33, 4]
        var sum = 0, avg = 0
        for (var i = 0; i < arr1.length; i++) {
            sum += arr1[i]
        }
        console.log(sum);
        avg = sum / (arr1.length)
        console.log(avg);
 
        //2、var str = 'qwfvsdbwqqabksh1jdjiirhbzfhtq';
        //（1）字符q出现的次数
        var count = 0, str2 = 'qwfvsdbwqqabksh1jdjiirhbzfhtq'
        for (var i = 0; i < str2.length; i++) {
            if (str2[i] == 'q') {
                count += 1
            }
        }
        console.log(count);
 
        //（2）统计每个字符出现的次数
        var str2 = 'qwfvsdbwqqabksh1jdjiirhbzfhtq', str3 = ''
        var count = {};
        for (var i = 0; i < str2.length; i++) {
            if (count[str2[i]]) {
                count[str2[i]]++;
            } else {
                count[str2[i]] = 1;
            }
        }
        console.log(count);
 
        //3、封装一个格式化日期的方法
        //法1
        var date = new Date()
        var str = ''
        str = date.getFullYear() + '-' + (date.getMonth() + 1) + '-' + date.getDate()
        console.log(str);
        //法2
        var a = '', b = '', c = ''
        function getdate(y, m, d) {
            var date = new Date();
            var y = date.getFullYear();
            var m = date.getMonth() + 1;
            var d = date.getDate();
            console.log(y + '-' + m + '-' + d);
        }
        getdate(a, b, c)
 
        //4、数组去重
        var arr4 = [1, 2, 3, 4, 4, 5, 6, 7, 7, 7, 8, 9, 3, 3, 4, 5, 6, 7, 9]
        var newArr = '';
        for (var i = 0; i < arr4.length; i++) {
            if (newArr.lastIndexOf(arr4[i]) == -1) {
                newArr += arr4[i];
            }
        }
        console.log(newArr);
 
        //5、返回随机1-100的整数
        console.log(Math.round(Math.random() * 100));
 
    </script>