Javascript’s toFixed Implementation without Rounding
- 时间:2020-09-24 11:54:15
- 分类:网络文摘
- 阅读:67 次

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:How to Find and Hire a Ghostwriter for Your Blog Showcase About the Best 30+ Web Tools and Services on the Market 3 Incredible Landing Pages And What We Can Learn From Them What is Cycle Counting and How to Implement It in Your Retail Bu 4 Reasons Why Your Blog is Struggling to Find an Audience 6 Best Fashion Bloggers for Style Inspiration The Strategy You Need to Write Better Blog Posts Than Your Compe How to Improve Your Blog’s Bounce Rate (and Why You Should) Does Your SME Have A Disaster Recovery Plan? 7 Best SEO Trends Gaining Popularity In 2019
- 评论列表
-
- 添加评论