先端学習ノート(三)Javascript文字列関数配列関数

/*
            0,          1
            
 */
testCharAt() {
     
    const str = "Hello World!";
    let a = str.charAt(0);//H
    let b = str.charAt(30);//""
    console.log(a);
    console.log(b);
},
//          ，        。
testConcat() {
     
    let a = "Hello ";
    let b = "World";
    let c = a.concat(b);
    console.log(a);//Hello
    console.log(b);//World
    console.log(c);//Hello World
},
//                       。
//      -1
testIndexOf() {
     
    let a = "Hello World";
    console.log(a.indexOf("ll"));//2
    console.log(a.indexOf(" "));//5
    console.log(a.indexOf("Wor"));//6
    console.log(a.indexOf("wor"));//-1
    console.log(a.indexOf("www"));//-1
},
//                 
testIncludes() {
     
    let a = "Hello World";
    console.log(a.includes("Wor"));//true
    console.log(a.includes("wor"));//false
},
testLastIndexOf() {
     
    let a = "Hello World";
    console.log(a.lastIndexOf("Wor"));//6
    console.log(a.lastIndexOf("wor"));//-1
},
testReplace() {
     
    let a = "Hello World";
    console.log(a.replace("World", "Pigg"));//Hello Pigg
},
//slice(start, end)              ，               。
//   start（  ）   end（   ）              。
//             0,          1,     。
testSlice() {
     
    let a = "Hello World";
    let b = a.slice(1, 3);
    console.log(a);//Hello World
    console.log(b);//el
},
//              
testSplit() {
     
    let a = "Hello World";
    let b = a.split(" ");
    console.log(a);//Hello World
    console.log(b);//["Hello", "World"]
},
testStartsWith() {
     
    let a = "Hello World";
    console.log(a.startsWith("Hel"));//true
    console.log(a.startsWith("hel"));//false
},
//substr()                            。
//statr    。           。     
//     length  。       。     。        ，      stringObject            。
testSubstr() {
     
    let a = "Hello World";
    let b = a.substr(1, 3);
    let c = a.substr(1);
    console.log(a);//Hello World
    console.log(b);//ell
    console.log(c);//ello World
},
//substring()                        。
//substring()                  ，            。
testSubstring() {
     
    let a = "Hello World";
    let b = a.substring(1, 3);
    let c = a.substring(1);
    console.log(a);//Hello World
    console.log(b);//el
    console.log(c);//ello World
}

    let vm = new Vue({
     
        el: "#app1",
        data: {
     
            arr: [1, 2, 3, 4],
            message: "hello vue.js!!!"
        },
        methods: {
     
            checkMoreThanTwo(num) {
     
                return num > 2;
            },
            //concat()              。
            //            ，                。
            testContact() {
     
                let a = ["a", "aa"];
                let b = ["b", "bb"];
                let c = a.concat(b);
                console.log(a);//["a", "aa"]
                console.log(b);//["b", "bb"]
                console.log(c);//["a", "aa", "b", "bb"]
            },
            //                
            testIncludes() {
     
                let a = ["a", "aa"];
                console.log(a.includes("a"));//true
                console.log(a.includes("aaa"));//false
            },
            //               ，         。
            //map       ，       
            //        
            testMap() {
     
                let newMapArr = this.arr.map(function (item) {
     
                    return item * 2;
                })
                this.message = newMapArr;
            },
            //                   
            testPop() {
     
                let a = ["a", "aa"];
                let b = a.pop();
                console.log(a);//["a"]
                console.log(b);//aa
            },
            //push()                   ，       
            testPush() {
     
                let a = ["a", "aa"];
                let b = a.push("aaa", "aaaa");
                console.log(a);//["a", "aa", "aaa", "aaaa"]
                console.log(b);//4
            },
            testFind() {
     
                //find             
                let arr2 = this.arr.find((n) => n > 1);
                this.message = arr2;
            },
            testFindIndex() {
     
                //findIndex               ，index 0  
                let index = this.arr.findIndex((n) => n > 0);
                this.message = index;
            },
            testFilter() {
     
                //filter          
                let filterArr = this.arr.filter((n) => n > 3);
                this.message = filterArr;
            },
            testSome() {
     
                //            true
                let someMoreThanTwo = this.arr.some(this.checkMoreThanTwo);
                this.message = someMoreThanTwo;
            },
            testEvery() {
     
                //         true
                let allMoreThanTwo = this.arr.every(this.checkMoreThanTwo);
                this.message = allMoreThanTwo;
            },
            testForEach() {
     
                this.arr.forEach(function (item, index, input) {
     
                    input[index] = item * 2;
                })
                this.message = this.arr;
            }

        }
    });