JS基礎知識復習(一)

6118 ワード

1.JS変数:



    
    Title
    
        /**
         * JS           :
         * 1.      
         *      1.1   :number
         *      1.2    :String
         *      1.3    :boolean
         *      1.4       :null undefined
         * 2.      
         */
        var age = 18 , name = "  " , sex = " ";
        alert("    =" + name + ",  :" + sex + ",  :" + age);
        alert(typeof  name);

        for (let i = 0; i < 20; i++) {
            if (i % 5 == 0 && i != 0){
                break;
            }
            document.write(i + ";");
        }

        /**
         *   input         :
         * document         ,  JS input  ,      。
         */
        var _input = document.getElementById("demo");
        alert(_input.name);

        /**
         *     :   jQuery  。
         */
        window.onload = function (){
            _input = document.getElementById("demo");
            alert(_input.name);
        };

    




      2.関数:



    
    Title
    
        /**
         * arguments:                ,
         */
        function sum() {
            // alert(arguments);
            let p = arguments;
            alert(p.length);
            //         
            let arr = new Array(20);
            alert(arr instanceof Array);
            // arr.push("h");
            // alert(arr.length);
        }
        sum(1,2,3);
        /**
         *        
         */
        function mySort(p , mode) {
            // let newArray;
            //          
            if (p instanceof Array){
                if (mode == "" || mode == null || mode == undefined || mode == "asc"){
                    for (let i = 0; i < p.length; i++) {
                        let tmp ;
                        for (let j = i + 1; j < p.length; j++) {
                            if (p[i] > p[j]){
                                tmp = p[i];
                                p[i] = p[j];
                                p[j] = tmp;
                            }
                        }
                    }
                }else if (mode == "desc"){
                    for (let i = 0; i < p.length; i++) {
                        let tmp ;
                        for (let j = i + 1; j < p.length; j++) {
                            if (p[i] < p[j]){
                                tmp = p[i];
                                p[i] = p[j];
                                p[j] = tmp;
                            }
                        }
                    }
                }

            }
            return p;
        }

        var demo = [4,5,8,1,9 ,5 ,0 , 10 , 100 , 20 , 31];
        demo = mySort(demo , '');
        alert(demo);
    




     3.配列常用関数:



    
    Title
    
        var arr = [10,20,30];
        var strArr = ["123" , "hello"];
        /**
         * forEach:    
         */
        strArr.forEach(function (value , index , array) {
            alert("  :" + index + ";  = " + value + ";   = " + array);
        });
        /**
         * map:      -  -  
         */
        var newArr = arr.map(function (value, index, array) {
            return value + 2;
        });
        alert("    = " + arr + "    = " + newArr);

        /**
         * filter:   
         * @type {number[]}
         */
        var arrFilter = arr.filter(function (value , index , array) {
            return value >20;
        });
        alert("       = " + arrFilter);

        /**
         * some:      ,  return       ,    true,     false
         *   :some         ,      ,   true,      !
         */
        var arrCheck = arr.some(function (value, index, array) {
            return value == 20;
        });
        alert(arrCheck);

        /**
         * every: some    ,           return   ,   true。         ,   false,    
         */
        var arrEvery = arr.every(function (value, index, array) {
            return value > 10;
        });
        alert("arr       10 ?" + arrEvery);
    




     4.Mathオブジェクト:



    
    Title
    
        /**
         * Math          
         */

        /**
         * Math.round:      
         */
        alert(Math.round(3.521313));

        /**
         * Math.random:0~1      
         */
        alert(Math.random());

        alert(Math.max(1,2,10,100)); //    ,min:   

        alert(Math.abs(-1)); //    

        alert(Math.ceil(3.1545));  //    
        alert(Math.floor(3.1545)); //    

        /**
         * Math.pow(x , y): X y  
         */
        alert(Math.pow(2,3));

        alert(Math.sqrt(4)); //    

        /**
         * Math       :sin、cos、tan、
         *      :      。Math.PI = 180  。  1   = Math.PI / 180
         */
        alert(Math.sin(30 * Math.PI / 180));
        alert(Math.cos(60 * Math.PI / 180));
    




    5.オブジェクト:



    
    Title
    
        /**
         *         
         */
            // 1.   new     
        var obj = new Object();
        obj.name = "  ";
        obj.age = 18;
        obj.getName = function () {
            return this.name;
        };

        alert(obj.getName());

        // 2. new     
        // 3.         
        var _obj = {};
        _obj.name = "  ";
        _obj.age = 20;
        _obj.setName = function (p) {
            this.name = p;
        };
        _obj.getName = function () {
            return this.name;
        }

        _obj.setName("  ");
        alert(_obj.getName());

        // delete        
        delete _obj.age;
        alert(_obj.age);