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This article introduces the relevant knowledge of "how to solve the pit of toFixed () and regular expressions in JavaScript". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

ToFixed accuracy problem

The toFixed method rounds Number to a specified number of decimal places. But if you look at the picture below, what do you find?

0.985 is rounded to 0.98 dollars!

This is the pit of the toFixed method.

Cause

So what's going on here? In essence, it is due to the accuracy of js decimals. To calculate in a computer is to convert the number to binary and then to decimal after calculation. For example, converting 0.985 to binary is 0.1111110000101000 (out of precision, the result retains 16 decimal places), and then converting the binary to decimal results is 0.9849853515625. At this time, keeping it with two decimal places becomes 0.98.

Solution.

So how to avoid this problem? You can supplement the native toFixed method with the following methods

ToFixed (number, precision) {var str = number + ""; var len = str.length; var last = str.substring (len-1, len); var afterPoint = str.substring (str.indexOf (".") + 1, len); if (last = "5" & & afterPoint.length > precision) {last = "6"; str = str.substring (0, len-1) + last; return (str-0) .tofixed (precision) } else {return number.toFixed (precision);}}, the pit for global matching of regular expressions

There is a need for select support to search for item. As soon as I saw it, I was excited to write, isn't it easy? the input data is regularly matched with the data source in select, and the match is found.

The filter function is what I wrote:

/ / searchKey is the input data const regex = new RegExp (searchKey.trim (), 'gi'); let dataSource = [{value:' test1',}, {value: 'test2',},]; let res = dataSource .map ((I) = > {let _ flag = regex.test (i.value); i.visible = _ flag; return i) }) .filter ((I) = > i.visible)

However, in the actual operation, it is found that some of the data in the data source can be matched and some can not. I wondered at that time, is there a problem? Finally, after looking for the answer, it turns out that there is a pit in the global matching of the regular expression: there is an attribute of lastIndex in the regular expression, which indicates the position of the first character after the last matching text result. On his next search, he will continue to search from lastIndex, which will cause the next match to return false.

So how to solve it?

Because the lastIndex attribute is readable and writable, my solution here is to set lastIndex to zero after each test method, so that each match will be looked up from the beginning. This will avoid this problem!

Let _ flag = regex.test (i.value); regex.lastIndex = 0; "how to solve the pits of toFixed () and regular expressions in JavaScript" ends here. Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

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