JavaScript: Trim.toPrecision () trailing zeros

Question

I am creating an online calculator using JavaScript.

I have this to work out the calculation:

eval(expression).toPrecision(10); 

This gives the correct conclusion in almost all cases. For instance.

 eval('456456+45646486*45646884').toPrecision(10) // Output: "2.083619852e+15" eval('1/0').toPrecision(10) // Output: "Infinity" 

but

 eval('4*1').toPrecision(10) // Output: "4.000000000" 

How to trim trailing zeros , but also keep good outputs higher?

Answer 1

decimal integers only

  eval('4*1').toPrecision(10).replace(/\.0+$/,"") 

null decimal numbers:

  eval('4.5*1').toPrecision(10).replace(/\.([^0]+)0+$/,".$1") 

edit: handle all null and null ending cases

EDIT: if you always use .toPrecision () and thus always have a ".", You can trim any trailing zeros:

  eval('4.5*1').toPrecision(10).replace(/0+$/,"") 

EDIT: trailing decimal places:

 eval('4.5*0').toPrecision(10).replace(/\.?0+$/,"") 

Answer 2

Divide by 1 after using toPrecision. Javascript will track zeros and no regular expressions are needed.

Answer 3

The next call to replace() will replace all trailing 0 and trailing . , if they are:

 eval(expression).toPrecision(10).replace(/(?:\.0+|(\.\d+?)0+)$/, "$1") 

How it works?

/(?:\.0+|(\.\d+?)0+)$/ searches for \.0+ or (\.\d+?)0+ at the end of the line ( $ ). ?: prevents \.0+|(\.\d+?)0+ from "capture" .

\.0+ will match . followed by any number 0 s.

(\.\d+?)0+ will match . followed by at least one digit, followed by at least one 0 . ? guarantees 0+ as large as 0 . The brackets "capture" are not 0 s.

The second replace() parameter is a new line to replace what was matched. $1 is a sorting variable and tells replace() to replace the matching value with the first committed value (since 1 was after $ ). In this case, the first recorded value was any \.\d+? .

So at the end:

• . followed by any number 0 will be discarded
• . followed by not 0 , followed by 0 , will be reset to 0

Examples

For comparing methods for accuracy 1 , 2 and 3 for .40*1 , 4*1 and 40*1 see below. The first (bold) element in each group is the method. Red elements are those that do not meet expectations.

 var tests = [ '.04*1', '.40*1', '4*1', '40*1' ]; var results = {}; for (var i = 0; i < tests.length; i += 1) { results[i] = {}; for (var p = 1; p < 3; p += 1) { results[i][p] = {}; results[i][p][0] = { 'output': eval(tests[i]).toPrecision(p).replace(/(?:\.0+|(\.\d+?)0+)$/, "$1"), 'regex': '/(?:\.0+|(\.\d+?)0+)$/, "$1"' }; results[i][p][1] = { 'output': eval(tests[i]).toPrecision(p).replace(/\.0+$/, ""), 'regex': '/\.0+$/, ""' }; results[i][p][2] = { 'output': eval(tests[i]).toPrecision(p).replace(/\.([^0]+)0+$/, ".$1"), 'regex': '/\.([^0]+)0+$/, ".$1"' }; results[i][p][3] = { 'output': eval(tests[i]).toPrecision(p).replace(/0+$/, ""), 'regex': '/0+$/, ""' }; results[i][p][4] = { 'output': eval(tests[i]).toPrecision(p).replace(/\.?0+$/, ""), 'regex': '/\.?0+$/, ""' }; } } for (var i in results) { $("#result").append("<h1>" + tests[i] + "</h1>"); for (var p in results[i]) { var expected = null; for (var t in results[i][p]) { var div = $("<div></div>"); if (t == 0) { expected = results[i][p][t].output; div.addClass("expected"); } else if (results[i][p][t].output !== expected) { div.addClass("invalid"); } div.append("P" + p + ": " + results[i][p][t].output); div.append(" <small>" + results[i][p][t].regex + "</small>"); $("#result").append(div); } $("#result").append("<br>"); } } 

 body { font-family: monospace; } .expected { font-weight: bold; } .invalid { color: red; } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script> <div id="result"></div>