Array对象常用方法

比眉伴天荒 2022-06-12 03:53 257阅读 0赞

//shift:删除原数组的第一项，返回删除元素的值；如果数组为空则返回undefined
        var arr = [1, 2, 3, 4, 5];
        var out = arr.shift();
        console.log(arr); //[2,3,4,5]
        console.log(out); //1
        var arr = [];
        var out = arr.shift();
        console.log(arr); //[]
        console.log(out); //undefined
    
    
        //unshift:将参数添加到原数组开头，返回数组的长度(ie6下返回undefined)
        var arr = [1, 2];
        var out = arr.unshift(-1, 0);
        console.log(arr); //[-1,0,1,2]
        console.log(out); //4
    
    
        //pop:删除原数组的最后一项，返回数组删除的值；如果数组为空则返回undefined
        var arr = [1, 2, 3, 4, 5];
        var out = arr.pop();
        console.log(arr); //[1,2,3,4]
        console.log(out); //5
        var arr = [];
        var out = arr.pop();
        console.log(arr); //[]
        console.log(out); //undefined
    
    
        //push:将参数添加到原数组的末尾，返回数组的长度
        var arr = [1, 2, 3];
        var out = arr.push(4, 5, 6);
        console.log(arr); //[1,2,3,4,5,6]
        console.log(out); //6
    
    
        //concat:返回一个将参数添加到原数组中构成的新数组
        var arr = [1, 2, 3];
        var out = arr.concat(4, 5);
        console.log(arr); //[1,2,3]
        console.log(out); //[1,2,3,4,5]
    
    
        //splice(start,deleteCount,val1,val2,...):从start位置开始删除原数组deleteCount项，并从该位置起插入val1,val2,...，返回删除的项组成的新数组
        var arr = [1, 2, 3, 4, 5];
        var out = arr.splice(2, 2, 7, 8, 9, 10);
        console.log(arr); //[1,2,7,8,9,10,5]
        console.log(out); //[3,4]
        //在清空数组时仅需传递start，如果不删除所有元素，再传递deleteCount
        var arr = [1, 2, 3, 4, 5];
        var out = arr.splice(2);
        console.log(arr); //[1,2]
        console.log(out); //[3,4,5]
        //同shift
        var arr = [1, 2, 3, 4, 5];
        var out = arr.splice(0, 1);
        console.log(arr); //[2,3,4,5]
        console.log(out); //[1]
        //同unshift
        var arr = [1, 2, 3, 4, 5];
        var out = arr.splice(0, 0, 22, -1, 0);
        console.log(arr); //[22,-1,0,1,2,3,4,5]
        console.log(out); //[]
        //同pop
        var arr = [1, 2, 3, 4, 5];
        var out = arr.splice(arr.length - 1, 1);
        console.log(arr); //[1,2,3,4]
        console.log(out); //[5]
        //同push
        var arr = [1, 2, 3, 4, 5];
        var out = arr.splice(arr.length, 0, 6, 7, 8);
        console.log(arr); //[1,2,3,4,5,6,7,8]
        console.log(out); //[]
    
    
        //reverse:将原数组倒序；
        var arr = ['a', 1, {}, [2, 3]];
        console.log(arr); //['a', 1, {}, [2, 3]]
        var out = arr.reverse();
        console.log(arr); //[[2,3],{},1,'a']
        console.log(out); //[[2,3],{},1,'a']
        var arr = [0, 1, 5, 10, 15];
        arr.reverse();
        console.log(arr); //[15,10,5,1,0]
        var arr = [1, 0, 5, 15, 10];
        arr.reverse();
        console.log(arr); //[10,15,5,0,1]
    
    
        //sort(orderfunction):sort()为升序排列，但是先调用每个数组项的toString()方法，然后比较字符串来排序，是按ASCII进行比较的；
        //所以跟reverse不同原理不同。sort()不带参数的时候是从字面上对数组排序
        var arr = [0, 1, 5, 10, 15];
        arr.sort();
        console.log(arr); //0,1,10,15,5 ,注意这里是字符串按ASCII进行比较的
        //调用这样的函数就按数值方式排列了
        function sortNumber(a, b) {
            return a - b
        }
        arr.sort(sortNumber);
        console.log(arr);   //0,1,5,10,15
    
    
        //slice(start,end):返回从原数组中指定start到end(不包含该元素)之间的项组成的新数组,如只有一个参数，则从start到数组末尾
        var arr = [1, 2, 3, 4, 5, 6, 7, 8];
        var out = arr.slice(2,3);
        console.log(arr); //[1, 2, 3, 4, 5, 6, 7, 8]
        console.log(out); //[3]
    
    
        //join(separator):将数组的元素组成一个字符串，以separator为分隔符，省略的话则用默认用逗号为分隔符
        var arr = [1, 2, 3, 4, 5, 6];
        var out = arr.join();
        console.log(arr); //[1, 2, 3, 4, 5, 6]
        console.log(out); //1,2,3,4,5,6
        out = arr.join("");
        console.log(out); //123456
        out = arr.join("&");
        console.log(out); //1&2&3&4&5&6