字符串前补0的几种方法

//填充数组

Array(5).fill(0) 如果没有fill(0),则为空值,所以有:

Array(5).jion(0)  是字符串

//字串或数组截取后几位

[1, 2, 3, 4, 5, 6, 7, 8, 9].slice(-3)

'hello world'.slice(-4)

//字符串前补0

//(Array(zeroNum).join(0)+num).slice(length)

var date = new Date();

var yyyy = date.getFullYear()

var month = (Array(3).join(0) + date.getMonth()).slice(-2)

var day = (Array(3).join(0) + date.getDay()).slice(-2)

var hh = (Array(3).join(0) + date.getHours()).slice(-2)

var MM = (Array(3).join(0) + date.getMinutes()).slice(-2)

var ss = (Array(3).join(0) + date.getSeconds()).slice(-2)

var ms = date.getMilliseconds()

var time = `${yyyy}-${month}-${day} ${hh}:${MM}:${ss}.${ms}`

console.log(time)

//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;

}