如何在 javascript 中将整数格式化为特定长度？

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I don't think there's anything "built" into the JavaScript language for doing this. Here's a simple function that does this:

function FormatNumberLength(num, length) {
var r = "" + num;
while (r.length < length) {
r = "0" + r;
}
return r;
}




FormatNumberLength(10000, 5) outputs '10000'
FormatNumberLength(1000, 5)  outputs '01000'
FormatNumberLength(100, 5)   outputs '00100'
FormatNumberLength(10, 5)    outputs '00010'

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This might help :

String.prototype.padLeft = function (length, character) {
return new Array(length - this.length + 1).join(character || '0') + this;
}


var num = '12';


alert(num.padLeft(4, '0'));

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You could go crazy with methods like these:

function PadDigits(input, totalDigits)
{
var result = input;
if (totalDigits > input.length)
{
for (i=0; i < (totalDigits - input.length); i++)
{
result = '0' + result;
}
}
return result;
}

But it won't make life easier. C# has a method like PadLeft and PadRight in the String class, unfortunately Javascript doesn't have this functionality build-in

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How about something like this:

function prefixZeros(number, maxDigits)
{
var length = maxDigits - number.toString().length;
if(length <= 0)
return number;


var leadingZeros = new Array(length + 1);
return leadingZeros.join('0') + number.toString();
}
//Call it like prefixZeros(100, 5); //Alerts 00100

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A funny (but interesting) way to prefix numbers with zeros:

function FormatInteger(num, length) {


return (num / Math.pow(10, length)).toFixed(length).substr(2);
}

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A "while" loop should make this easy enough.

function formatLength(a) {
var num = document.getElementById(a)
while (num.value.length < 4) {
num.value = '0' + num.value
}
}

That would loop through until the length of the num value reached 4 digits (assuming you have passed in the id of the number element as an argument)

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I ran into much the same problem and I found a compact way to solve it. If I had to use it multiple times in my code or if I was doing it for any more than four digits, I'd use one of the other suggested solutions, but this way lets me put it all in an expression:

((x<10)?"000": (x<100)?"00": (x<1000)?"0": "") + x

It's actually the same as your code, but using the ternary operator instead of "if-else" statements (and moving the "+ x", which will always be part of the expression, outside of the conditional code).

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The simplest way I can think of is this:

("000" + num).slice(-4)

A padded number is a string.
When you add a number to a string, it is converted to a string.
Strings has the method slice, that retuns a fixed length piece of the string.
If length is negative the returned string is sliced from the end of the string.

to test:

var num=12;
console.log(("000" + num).slice(-4)); // Will show "0012"

Of cause this only works for positive integers of up to 4 digits. A slightly more complex solution, will handle positive integers:

'0'.repeat( Math.max(4 - num.toString().length, 0)) + num

Create a string by repeat adding zeros, as long as the number of digits (length of string) is less than 4 Add the number, that is then converted to a string also.

Edit: from now on you should probably use this function:

String(num).padStart(4,'0')

It still doesn't handle negative numbers...

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Another one:

function format_number_length(num, length) {
var r = num.toString();
if (r.length<length) r = Array(length - r.length + 1).join('0') + r;
return r;
}

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I think the most compact yet intuitive way is:

function toFixedLength(input, length, padding) {
padding = String(padding || "0");
return (padding.repeat(length) + input).slice(-length);
}

The slice method here could be replaced with substr if that is more intuitive to the coder.

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I came looking for the answer, but I think this is a better functional approach (ES6):

const formatNumberToString = (num, minChars) => {
return num.toString().length < minChars
? formatNumberToString(`0${num}`, minChars)
: num.toString()
}
// formatNumberToString(12, 4) // "0012"
// formatNumberToString(12, 5) // "00012"
// formatNumberToString(1, 4) // "0001"
// formatNumberToString(1, 2) // "01"
// formatNumberToString(12, 2) // "12"
// formatNumberToString(12, 1) // "12"

also, this can be implemented just in one line

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最佳答案

Since ES2017 padding to a minimum length can be done simply with String.prototype.padStart and String.prototype.padEnd:

let number = 3
let string = number.toString().padStart(3, '0')
console.log(string) // "003"

Or if only the whole part of a float should be a fixed length:

let number = 3.141
let array = number.toString().split('.')
array[0] = array[0].padStart(3, '0')
let string = array.join('.')
console.log(string) // "003.141"

Neither of these simple uses handle sign, only showing a fraction part when number is not an integer, or other scenarios - so here is a simple example formatting function without options:

function format (number) {
let [ integer, fraction = '' ] = number.toString().split('.')
let sign = ''
if (integer.startsWith('-')) {
integer = integer.slice(1)
sign = '-'
}
integer = integer.padStart(3, '0')
if (fraction) {
fraction = '.' + fraction.padEnd(6, '0')
}
let string = sign + integer + fraction
return string
}


console.log(format(3)) // "003"
console.log(format(-3)) // "-003"
console.log(format(4096)) // "4096"
console.log(format(-3.141)) // "-003.141000"

Although notably this will not handle things that are not numbers, or numbers that toString into scientific notation.

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Latest with ES6 repeat() method:

    const length_required = 5;
let num = 10;
num = "0".repeat(length_required - String(num).length) + num;
console.log(num)
// output: 00010


let num = 1000;
num = "0".repeat(length_required - String(num).length) + num;
console.log(num)
// output: 01000

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I know this question is kind of old, but for anyone looking for something similar to String formatting on Java or Python, I have these helper methods:

String.format = (...args) => {
if( args.length == 0 ){
throw new Error("String format error: You must provide at least one argument");
}
const delimiter = "@LIMIT*";
const format = String(args.shift(1,0)).replace(/(%[0-9]{0,}[sd])/g, delimiter+"$1"+delimiter).split(delimiter); // First element is the format
if( [...format].filter(el=>el.indexOf("%")>-1).length != args.length ){
throw new Error("String format error: Arguments must match pattern");
}
if( format.length == 1 && args.length == 0 ){
return String(format);
}
let formattedString = "";
// patterns
const decimalPattern = /%[0-9]{0,}d/;
const stringPattern  = /%s/;
if( format.length == 0 ){
throw new Error("String format error: Invalid format");
}
let value        = null;
let indexOfParam = 0;
let currPattern  = null;
while( args.length > 0 ) {
currPattern = format[indexOfParam];
indexOfParam++;
if( currPattern.indexOf("%")<0 ){
formattedString+=currPattern;
continue;
}
value = args.shift(0,1);
if( decimalPattern.test(currPattern) ){
let numberLength = parseInt(currPattern.replace(/[^0-9]/g,''));
if( isNaN(numberLength) ){
numberLength = 0;
}
formattedString+=numberToLength(value, numberLength);
} else if( stringPattern.test(currPattern) ) {
if( typeof value === 'object' && value.toSource ){
formattedString+=String(value.toSource());
} else {
formattedString+=String(value);
}
} else {
throw new Error("String format error: Unrecognized pattern:"+currPattern);
}
}
return formattedString;
}


const numberToLength = (number, length) => {
length = parseInt(length);
number = String(number);
if( isNaN(length) || isNaN(parseInt(number)) ){
throw new Error("Invalid number passed");
}
while( number.length < length ) {
number = "0" + number;
}
return number;
}

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Another way is the Internationalization API:

const digits3 =
new Intl.NumberFormat(
undefined,
{ minimumIntegerDigits: 3, maximumSignificantDigits: 3 });


digits3.format(42);

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat/NumberFormat

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In JavaScript we have string method padStart.

This is example from https://www.w3schools.com/js/js_string_methods.asp

let numb = 5;
let text = numb.toString();
let padded = text.padStart(4, "0");