如何在 JavaScript 中用逗号打印一个数字作为千位

问题描述

我正在尝试在 JavaScript 中打印一个整数，并用逗号作为千位分隔符.例如，我想将数字 1234567 显示为1,234,567".我该怎么做呢?

I am trying to print an integer in JavaScript with commas as thousands separators. For example, I want to show the number 1234567 as "1,234,567". How would I go about doing this?

这是我的做法:

function numberWithCommas(x) {
    x = x.toString();
    var pattern = /(-?d+)(d{3})/;
    while (pattern.test(x))
        x = x.replace(pattern, "$1,$2");
    return x;
}

有没有更简单或更优雅的方法来做到这一点?如果它也适用于浮点数会很好，但这不是必需的.在句点和逗号之间决定不需要特定于语言环境.

Is there a simpler or more elegant way to do it? It would be nice if it works with floats also, but that is not necessary. It does not need to be locale-specific to decide between periods and commas.

推荐答案

我使用了 Kerry 的回答中的想法，但简化了它，因为我只是为我的特定目的寻找简单的东西.这是我所拥有的:

I used the idea from Kerry's answer, but simplified it since I was just looking for something simple for my specific purpose. Here is what I have:

function numberWithCommas(x) {
    return x.toString().replace(/B(?=(d{3})+(?!d))/g, ",");
}

function numberWithCommas(x) {
    return x.toString().replace(/B(?<!.d*)(?=(d{3})+(?!d))/g, ",");
}

function test(x, expect) {
    const result = numberWithCommas(x);
    const pass = result === expect;
    console.log(`${pass ? "✓" : "ERROR ====>"} ${x} => ${result}`);
    return pass;
}

let failures = 0;
failures += !test(0,        "0");
failures += !test(100,      "100");
failures += !test(1000,     "1,000");
failures += !test(10000,    "10,000");
failures += !test(100000,   "100,000");
failures += !test(1000000,  "1,000,000");
failures += !test(10000000, "10,000,000");
if (failures) {
    console.log(`${failures} test(s) failed`);
} else {
    console.log("All tests passed");
}

.as-console-wrapper {
    max-height: 100% !important;
}

正则表达式使用 2 个前瞻断言:

The regex uses 2 lookahead assertions:

• 一个正数，用于查找字符串中后面连续有 3 个数字的倍数的任何点，
• 一个否定断言，以确保该点仅具有 3 位数字的倍数.替换表达式在此处放置一个逗号.

例如，如果你传递它 123456789.01，肯定断言将匹配 7 左边的每个点(因为 789 是 3 位的倍数，678 是 3 位的倍数，567 等).否定断言检查 3 位的倍数后面没有任何数字.789 后面有一个句点，所以它正好是 3 位数字的倍数，所以用逗号.678 是 3 位数字的倍数，但它后面有一个 9，所以这 3 位数字是一组 4 的一部分，逗号不会去那里.567 也是如此.456789 是 6 位数字，是 3 的倍数，所以前面要加逗号.345678 是 3 的倍数，但它后面有一个 9，所以那里没有逗号.等等.B 防止正则表达式在字符串开头放置逗号.

For example, if you pass it 123456789.01, the positive assertion will match every spot to the left of the 7 (since 789 is a multiple of 3 digits, 678 is a multiple of 3 digits, 567, etc.). The negative assertion checks that the multiple of 3 digits does not have any digits after it. 789 has a period after it so it is exactly a multiple of 3 digits, so a comma goes there. 678 is a multiple of 3 digits but it has a 9 after it, so those 3 digits are part of a group of 4, and a comma does not go there. Similarly for 567. 456789 is 6 digits, which is a multiple of 3, so a comma goes before that. 345678 is a multiple of 3, but it has a 9 after it, so no comma goes there. And so on. The B keeps the regex from putting a comma at the beginning of the string.

@neu-rah 提到如果后面有超过 3 个数字，这个函数会在不需要的地方添加逗号小数点.如果这是一个问题，你可以使用这个功能:

@neu-rah mentioned that this function adds commas in undesirable places if there are more than 3 digits after the decimal point. If this is a problem, you can use this function:

function numberWithCommas(x) {
    var parts = x.toString().split(".");
    parts[0] = parts[0].replace(/B(?=(d{3})+(?!d))/g, ",");
    return parts.join(".");
}

function numberWithCommas(x) {
    var parts = x.toString().split(".");
    parts[0] = parts[0].replace(/B(?=(d{3})+(?!d))/g, ",");
    return parts.join(".");
}

function test(x, expect) {
    const result = numberWithCommas(x);
    const pass = result === expect;
    console.log(`${pass ? "✓" : "ERROR ====>"} ${x} => ${result}`);
    return pass;
}

let failures = 0;
failures += !test(0              , "0");
failures += !test(0.123456       , "0.123456");
failures += !test(100            , "100");
failures += !test(100.123456     , "100.123456");
failures += !test(1000           , "1,000");
failures += !test(1000.123456    , "1,000.123456");
failures += !test(10000          , "10,000");
failures += !test(10000.123456   , "10,000.123456");
failures += !test(100000         , "100,000");
failures += !test(100000.123456  , "100,000.123456");
failures += !test(1000000        , "1,000,000");
failures += !test(1000000.123456 , "1,000,000.123456");
failures += !test(10000000       , "10,000,000");
failures += !test(10000000.123456, "10,000,000.123456");
if (failures) {
    console.log(`${failures} test(s) failed`);
} else {
    console.log("All tests passed");
}

.as-console-wrapper {
    max-height: 100% !important;
}

@tjcrowder 指出，现在 JavaScript 有lookbehind (支持信息)，可以在正则表达式本身解决:

@t.j.crowder pointed out that now that JavaScript has lookbehind (support info), it can be solved in the regular expression itself:

function numberWithCommas(x) {
    return x.toString().replace(/B(?<!.d*)(?=(d{3})+(?!d))/g, ",");
}

function numberWithCommas(x) {
    return x.toString().replace(/B(?<!.d*)(?=(d{3})+(?!d))/g, ",");
}

function test(x, expect) {
    const result = numberWithCommas(x);
    const pass = result === expect;
    console.log(`${pass ? "✓" : "ERROR ====>"} ${x} => ${result}`);
    return pass;
}

let failures = 0;
failures += !test(0,               "0");
failures += !test(0.123456,        "0.123456");
failures += !test(100,             "100");
failures += !test(100.123456,      "100.123456");
failures += !test(1000,            "1,000");
failures += !test(1000.123456,     "1,000.123456");
failures += !test(10000,           "10,000");
failures += !test(10000.123456,    "10,000.123456");
failures += !test(100000,          "100,000");
failures += !test(100000.123456,   "100,000.123456");
failures += !test(1000000,         "1,000,000");
failures += !test(1000000.123456,  "1,000,000.123456");
failures += !test(10000000,        "10,000,000");
failures += !test(10000000.123456, "10,000,000.123456");
if (failures) {
    console.log(`${failures} test(s) failed`);
} else {
    console.log("All tests passed");
}

.as-console-wrapper {
    max-height: 100% !important;
}

(?<!.d*) 是一个否定的lookbehind，表示匹配项前面不能有 . 后跟零个或多个数字.负面的lookbehind比split和join解决方案更快(比较)，至少在 V8 中.

(?<!.d*) is a negative lookbehind that says the match can't be preceded by a . followed by zero or more digits. The negative lookbehind is faster than the split and join solution (comparison), at least in V8.

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