JS round to 2 decimal places [duplicate]

问题

This question already has answers here:

Round to at most 2 decimal places (only if necessary) (72 answers)

Closed 4 years ago.

I am trying to limit the returned number to be only 2 decimal places but this code isn't working for me;

function myFunction() {
var x = document.getElementById("mySelect").value;
document.getElementById("demo").innerHTML = "Result is: " + x * 1.09; value = valToRound.toFixed(2);

}

What am I doing wrong?

回答1:

Typing in the JS Browser console

  x = 2.71828
  x.toFixed(2)
  "2.72"

it is clear that .toFixed(2) works

What you did wrong was rounding after printing the answer, and not using the correct variables.

document.getElementById("demo").innerHTML = "Result is: " + x * 1.09; value = valToRound.toFixed(2);

It is also a good idea to get in the habit of converting strings to numbers with parseFloat(). In JS, '2'*'2' is '4' but '2'+'2' is '22', unless you first convert to number.

If you do it this way it will work:

function myFunction() {
  var x = parseFloat(document.getElementById("mySelect").value);
  var valToRound = x * 1.09;
  var value = valToRound.toFixed(2);
  document.getElementByID("demo").innerHTML = "Result is: " + value;
}

来源：https://stackoverflow.com/questions/32300649/js-round-to-2-decimal-places