ここにいくつかのソリューションがあります。すべてテストスイートに合格し、テストスイートとベンチマークが含まれています。コピーして貼り付けてテストする場合は、この要点を試してください。
方法0（RegExp）
https://stackoverflow.com/a/14428340/1877620に基づいていますが、小数点がない場合は修正してください。
if (typeof Number.prototype.format === 'undefined') {
Number.prototype.format = function (precision) {
if (!isFinite(this)) {
return this.toString();
}
var a = this.toFixed(precision).split('.');
a[0] = a[0].replace(/\d(?=(\d{3})+$)/g, '$&,');
return a.join('.');
}
}
方法1
if (typeof Number.prototype.format === 'undefined') {
Number.prototype.format = function (precision) {
if (!isFinite(this)) {
return this.toString();
}
var a = this.toFixed(precision).split('.'),
// skip the '-' sign
head = Number(this < 0);
// skip the digits that's before the first thousands separator
head += (a[0].length - head) % 3 || 3;
a[0] = a[0].slice(0, head) + a[0].slice(head).replace(/\d{3}/g, ',$&');
return a.join('.');
};
}
方法2（配列に分割）
if (typeof Number.prototype.format === 'undefined') {
Number.prototype.format = function (precision) {
if (!isFinite(this)) {
return this.toString();
}
var a = this.toFixed(precision).split('.');
a[0] = a[0]
.split('').reverse().join('')
.replace(/\d{3}(?=\d)/g, '$&,')
.split('').reverse().join('');
return a.join('.');
};
}
方法3（ループ）
if (typeof Number.prototype.format === 'undefined') {
Number.prototype.format = function (precision) {
if (!isFinite(this)) {
return this.toString();
}
var a = this.toFixed(precision).split('');
a.push('.');
var i = a.indexOf('.') - 3;
while (i > 0 && a[i-1] !== '-') {
a.splice(i, 0, ',');
i -= 3;
}
a.pop();
return a.join('');
};
}
使用例
console.log('======== Demo ========')
console.log(
(1234567).format(0),
(1234.56).format(2),
(-1234.56).format(0)
);
var n = 0;
for (var i=1; i<20; i++) {
n = (n * 10) + (i % 10)/100;
console.log(n.format(2), (-n).format(2));
}
セパレーター
カスタムの桁区切り記号または小数点記号が必要な場合は、次を使用しますreplace()。
123456.78.format(2).replace(',', ' ').replace('.', ' ');
テストスイート
function assertEqual(a, b) {
if (a !== b) {
throw a + ' !== ' + b;
}
}
function test(format_function) {
console.log(format_function);
assertEqual('NaN', format_function.call(NaN, 0))
assertEqual('Infinity', format_function.call(Infinity, 0))
assertEqual('-Infinity', format_function.call(-Infinity, 0))
assertEqual('0', format_function.call(0, 0))
assertEqual('0.00', format_function.call(0, 2))
assertEqual('1', format_function.call(1, 0))
assertEqual('-1', format_function.call(-1, 0))
// decimal padding
assertEqual('1.00', format_function.call(1, 2))
assertEqual('-1.00', format_function.call(-1, 2))
// decimal rounding
assertEqual('0.12', format_function.call(0.123456, 2))
assertEqual('0.1235', format_function.call(0.123456, 4))
assertEqual('-0.12', format_function.call(-0.123456, 2))
assertEqual('-0.1235', format_function.call(-0.123456, 4))
// thousands separator
assertEqual('1,234', format_function.call(1234.123456, 0))
assertEqual('12,345', format_function.call(12345.123456, 0))
assertEqual('123,456', format_function.call(123456.123456, 0))
assertEqual('1,234,567', format_function.call(1234567.123456, 0))
assertEqual('12,345,678', format_function.call(12345678.123456, 0))
assertEqual('123,456,789', format_function.call(123456789.123456, 0))
assertEqual('-1,234', format_function.call(-1234.123456, 0))
assertEqual('-12,345', format_function.call(-12345.123456, 0))
assertEqual('-123,456', format_function.call(-123456.123456, 0))
assertEqual('-1,234,567', format_function.call(-1234567.123456, 0))
assertEqual('-12,345,678', format_function.call(-12345678.123456, 0))
assertEqual('-123,456,789', format_function.call(-123456789.123456, 0))
// thousands separator and decimal
assertEqual('1,234.12', format_function.call(1234.123456, 2))
assertEqual('12,345.12', format_function.call(12345.123456, 2))
assertEqual('123,456.12', format_function.call(123456.123456, 2))
assertEqual('1,234,567.12', format_function.call(1234567.123456, 2))
assertEqual('12,345,678.12', format_function.call(12345678.123456, 2))
assertEqual('123,456,789.12', format_function.call(123456789.123456, 2))
assertEqual('-1,234.12', format_function.call(-1234.123456, 2))
assertEqual('-12,345.12', format_function.call(-12345.123456, 2))
assertEqual('-123,456.12', format_function.call(-123456.123456, 2))
assertEqual('-1,234,567.12', format_function.call(-1234567.123456, 2))
assertEqual('-12,345,678.12', format_function.call(-12345678.123456, 2))
assertEqual('-123,456,789.12', format_function.call(-123456789.123456, 2))
}
console.log('======== Testing ========');
test(Number.prototype.format);
test(Number.prototype.format1);
test(Number.prototype.format2);
test(Number.prototype.format3);
基準
function benchmark(f) {
var start = new Date().getTime();
f();
return new Date().getTime() - start;
}
function benchmark_format(f) {
console.log(f);
time = benchmark(function () {
for (var i = 0; i < 100000; i++) {
f.call(123456789, 0);
f.call(123456789, 2);
}
});
console.log(time.format(0) + 'ms');
}
// if not using async, browser will stop responding while running.
// this will create a new thread to benchmark
async = [];
function next() {
setTimeout(function () {
f = async.shift();
f && f();
next();
}, 10);
}
console.log('======== Benchmark ========');
async.push(function () { benchmark_format(Number.prototype.format); });
next();
formatNumberJavaScriptには組み込み関数はありません