js中數據的用法總結

一，會改變原數組

1.移除數組末尾最後一項.pop()，返回刪除的元素 若是你在一個空數組上調用 pop()，它返回 undefined

let word = ['a', 'b', 'c', 'd'];

let newArr = word.pop();  
console.log(word);      //['a', 'b', 'c']  
console.log(newArr);    //d  

let nullArr = [];  
console.log(nullArr.pop()); //undefined 


        2.在數組末尾添加一個或多個元素.push()，返回修改後數組長度

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let word = ['a', 'b', 'c', 'd'];  
    let newArr = word.push('e','f');  
    console.log(word);      //['a', 'b', 'c', 'd', 'e', 'f']  
    console.log(newArr);    //6  
        3.移除數組第一項.shift()，返回移除的元素

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let word = ['a', 'b', 'c', 'd'];  
    let newArr = word.shift();  
    console.log(word);      //['b', 'c', 'd']  
    console.log(newArr);    //a  
        4.在數組頭部添加一個或多個元素.unshift()，返回修改後數組長度

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let word = ['a', 'b', 'c', 'd'];  
    let newArr = word.unshift('11','22');  
    console.log(word);      //['11', '22', 'a', 'b', 'c', 'd']  
    console.log(newArr);    //6  
        5.對數組元素排序.sort()，返回排序後的數組
            默認排序順序是根據字符串Unicode碼點

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let fruit = ['cherries', 'apples', 'bananas'];  
    console.log(fruit.sort());       // ['apples', 'bananas', 'cherries']  
      
    let scores = [1, 10, 21, 2];   
    console.log(scores.sort());  
    // [1, 10, 2, 21]  
    // 注意10在2以前,  
    // 由於在 Unicode 指針順序中"10"在"2"以前  

    let things = ['word', 'Word', '1 Word', '2 Words'];  
    console.log(things.sort());   
    // ['1 Word', '2 Words', 'Word', 'word']  
    // 在Unicode中, 數字在大寫字母以前,  
    // 大寫字母在小寫字母以前.  

    function compare(a, b) {  
        if(a < b) {  
            return -1;  
        }else if(a > b) {  
            return 1;  
        }else {  
            return 0;  
        }  
    }  
    let num = [1, 10, 21, 2];  
    console.log(num.sort(compare)); //[1, 2, 10, 21]  
        6.顛倒數組元素.reverse()，返回顛倒後的數組

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let word = ["a", "b", "c", "d"];  
    let newArr = word.reverse();  
    console.log(word);      //["d", "c", "b", "a"]  
    console.log(newArr);    //["d", "c", "b", "a"]  
        7.刪除或插入元素.splice()，返回數組刪除的項，沒有刪除的項，返回空數組

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var word = ['a', 'b', 'c', 'd'];  
    //刪除,前閉後開  
    var newArr = word.splice(0,2);  
    console.log(word);      //["c", "d"]  
    console.log(newArr);    //["a", "b"]  

    //插入,當前數組索引1處插入hello  
    var newArr = word.splice(1,0,'hello');  
    console.log(word);      //["c", "hello", "d"]  
    console.log(newArr);    //[]  

    //替換  
    var newArr = word.splice(1,1,'world');  
    console.log(word);      //["c", "world", "d"]  
    console.log(newArr);    //["hello"]