javascript - Math.log() inaccuracy - How to deal with it? -

this question has answer here:

• is floating point math broken? 20 answers

i know getting 10 based logarithm have use math.log() divided constant of natural logarithm of 10.

var e1000 = math.log(1000) / math.ln10;  // result: 2.9999999999999996 instead of  //   expected 3. console.log(e1000);   // result:  999.999999999999 instead of //   expected 1000. console.log(math.pow(10, e1000)); 

but: result approximation. if use calculated value in further calculation inaccuracy becomes worse.

am doing wrong? there more elegant way around using math.ceil()?

the floating point rounding difference known , coincidentally 2.9999 exact example used in mdn math.log page. mentioned math.ceiling can used alther result. likewise increase base number , use smaller divider decrease change of floating errors. e.g.

function log10(value){   return -3 * (math.log(value * 100)  / math.log(0.001))  - 2; } 

example: fiddle

as sidenote, browsers support math.log10 functionality, extend math use function above if not implemented with:

if (!math.log10) math.log10 = function(value){   return -3 * (math.log(value * 100)  / math.log(0.001))  - 2; }; 

after running initializer, can use math.log10() , code automatically use browser functionality (or when becomes) available. (fiddle)