Javascript’s toFixed Implementation without Rounding

  • 时间:2020-09-24 11:54:15
  • 分类:网络文摘
  • 阅读:126 次
JS Javascript's toFixed Implementation without Rounding javascript

NodeJs / Javascript

In Javascript, you can use Number.prototype.toFixed(n) that will return a string version that has n decimal places. For example,

1
2
(3).toFixed(3) // "3.000"
(3.15).toFixed(3) // "3.150"
(3).toFixed(3) // "3.000"
(3.15).toFixed(3) // "3.150"

The toFixed will round up the last digit (from 6 not 5):

1
2
(3.1595).toFixed(3) // "3.159"
(3.1596).toFixed(3) // "3.160"
(3.1595).toFixed(3) // "3.159"
(3.1596).toFixed(3) // "3.160"

If we don’t want to round-up the decimal values, we can to this thanks to Regular Expression Matching:

1
2
3
4
5
6
7
8
9
10
Number.prototype.toFixedNoRounding = function(n) {
    const reg = new RegExp("^-?\\d+(?:\\.\\d{0," + n + "})?", "g")
    const a = this.toString().match(reg)[0];
    const dot = a.indexOf(".");
    if (dot === -1) { // integer, insert decimal dot and pad up zeros
        return a + "." + "0".repeat(n);
    }
    const b = n - (a.length - dot) + 1;
    return b > 0 ? (a + "0".repeat(b)) : a;
 }
Number.prototype.toFixedNoRounding = function(n) {
    const reg = new RegExp("^-?\\d+(?:\\.\\d{0," + n + "})?", "g")
    const a = this.toString().match(reg)[0];
    const dot = a.indexOf(".");
    if (dot === -1) { // integer, insert decimal dot and pad up zeros
        return a + "." + "0".repeat(n);
    }
    const b = n - (a.length - dot) + 1;
    return b > 0 ? (a + "0".repeat(b)) : a;
 }

The idea is to convert the number into string (via toString()) and use the RegExp to truncate the extra zeros (without rounding). Next, we find out the position of decimal dot (if any), and pad up the zeros for exactly n decimal places. We compute the number of zeros we need and if it is positive, we use the String.prototype.repeat() to insert additional zeros at the end. We could also use the String.prototype.padEnd() which may seem a bit less intuitive.

1
2
3
4
5
6
7
console.log((3.1999).toFixedNoRounding(3));  // 3.199
console.log((3.19923413412349).toFixedNoRounding(3)); // 3.199
console.log((3.01).toFixedNoRounding(3)); // 3.010
console.log((3.01).toFixedNoRounding(4)); // 3.0100
console.log((3.01).toFixedNoRounding(5)); // 3.01000
console.log((3).toFixedNoRounding(3)); // 3.000
console.log((-3).toFixedNoRounding(3)); // -3.000
console.log((3.1999).toFixedNoRounding(3));  // 3.199
console.log((3.19923413412349).toFixedNoRounding(3)); // 3.199
console.log((3.01).toFixedNoRounding(3)); // 3.010
console.log((3.01).toFixedNoRounding(4)); // 3.0100
console.log((3.01).toFixedNoRounding(5)); // 3.01000
console.log((3).toFixedNoRounding(3)); // 3.000
console.log((-3).toFixedNoRounding(3)); // -3.000

–EOF (The Ultimate Computing & Technology Blog) —

推荐阅读:
Use jQuery Migrate Helper Plugin to Fix the Classic Editor Error  How to Fix CloudFlare Error 1101 (Worker threw exception)?  Python Function to Convert Excel Sheet Column Titles to Numbers  Algorithm to Find the Kth Missing Positive Number in Array  How to Partition a String into Palindromes using DFS Algorithm?  How to Get Blockchain Version of Steem RPC Node using Javascript  How to Find All Duplicates in an Array using Python?  Bruteforce and Rolling Hash Algorithm to Compute the Longest Hap  How to Choose the Right Products and Services to Blog About  Buying a Home as a Blogger 
评论列表
添加评论