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。
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<!DOCTYPE html PUBLIC
"-//W3C//DTD XHTML 1.0 Transitional//EN"
<head>
<meta http-equiv=
"Content-Type"
content=
"text/html; charset=utf-8"
/>
<title>JavaScript 数字前补“0”</title>
<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>
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输出
0000000123
0000000123
0000000123
0000000123
000000123
1234567890123
1234567890123
4567890123
4567890123
1234567890123