how to reduce numbers' significance in JSON's stringify

Question

I have an array with numbers (coordinates) and I want to display those using JSON like so

 JSON.stringify(array); 

My array looks like:

[{"x":-0.825,"y":0},  {"x":-1.5812500000000003,"y":-0.5625},  {"x":-2.2515625000000004,"y":-1.546875}] 

But I'm only interested in the first (lets say) 4 significant digits, i.e.

[{"x":-0.825,"y":0},  {"x":-1.5813,"y":-0.5625},  {"x":-2.2516,"y":-1.5469}] 

Is there a way to easily ditch the remaining insignificant numbers?

Answer 1

Native JSON.stringify accepts the parameter replacer, which can be a function converting values to whatever is needed:

a = [0.123456789123456789] JSON.stringify(a, function(key, val) {     return val.toFixed ? Number(val.toFixed(3)) : val; })  >> "[0.123]" 

Answer 2

Use Number#toPrecision or Number#toFixed, whichever suits your needs better. The difference is that toFixed sets the number of digits after the decimal point, and toPrecision sets the entire number of digits.

var foo = 1.98765432;  console.log(foo.toPrecision(5)); // 1.9877 

Note that toFixed and toPrecision return strings, so you'll probably want to convert them back to numbers before JSONifying them.

Here's the obligatory MDN link.

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You can also do something like this, if you want to roll your own.

Math.round(1.98765432 * 10000) / 10000 // 1.9877 

Encapsulated in a function, it might look something like this:

function precisify(n, places) {      var scale = Math.pow(10, places);      return Math.round(n * scale) / scale;  }