JavaScript 数字前补“0”的五种方法

傷城~ 2022-09-30 00:56 638阅读 0赞

众所周知JavaScript中的数字是没有前置0的，因此需要我们自己进行操作来添加前置0，而且还得转换成字符串。

<html>
    <body>
    <script>
        //迭代方式实现
        function padding1(num, length) { 
            for(var len = (num + "").length; len < length; len = num.length) {
                num = "0" + num;            
            }
            return num;
        }
    
        //递归方式实现
        function padding2(num, length) { 
            if((num + "").length >= length) {
                return num;
            }
            return padding2("0" + num, length)
        }
    
        //转为小数
        function padding3(num, length) { 
            var decimal = num / Math.pow(10, length);
            //toFixed指定保留几位小数
            decimal = decimal.toFixed(length) + "";
            return decimal.substr(decimal.indexOf(".")+1);
        }
    
        //填充截取法
        function padding4(num, length) { 
            //这里用slice和substr均可
            return (Array(length).join("0") + num).slice(-length);
        }
    
        //填充截取法
        function padding5(num, length) { 
            var len = (num + "").length;
            var diff = length - len;
            if(diff > 0) {
                return Array(diff).join("0") + num;
            }
            return num;
        }
    
        function test(num, length) { 
            document.write(padding1(num, length));
            document.write("<br>");
            document.write(padding2(num, length));
            document.write("<br>");
            document.write(padding3(num, length));
            document.write("<br>");
            document.write(padding4(num, length));
            document.write("<br>");
            document.write(padding5(num, length));
            document.write("<br>");
        }
    
        test(123, 10);
        test(1234567890123, 10);
    
    </script>
    </body>
    </html>

输出

0000000123
    0000000123
    0000000123
    0000000123
    000000123
    1234567890123
    1234567890123
    4567890123
    4567890123
    1234567890123