javascript - Math.round not returning integers as expected - Stack Overflow

admin管理员组

文章数量:1393392

I'm trying to edit an existing (working, shown first) script that delivers two decimals so that it will only deliver rounded numbers - my edit shown second (example). To be clear I want simple integers i.e. 18 not 18.00.

function D(r){
    if (r.stat === "ok") {
        for (var k in r.items) {
            document.write(r.items[k].inventory)
        }
    }
}

function D(r){
    if (r.stat === "ok") {
        for (var k in r.items) {
            document.write(r.items[k].inventory)
            Math.round()
        }
     }
}

I'm trying to edit an existing (working, shown first) script that delivers two decimals so that it will only deliver rounded numbers - my edit shown second (example). To be clear I want simple integers i.e. 18 not 18.00.

function D(r){
    if (r.stat === "ok") {
        for (var k in r.items) {
            document.write(r.items[k].inventory)
        }
    }
}

function D(r){
    if (r.stat === "ok") {
        for (var k in r.items) {
            document.write(r.items[k].inventory)
            Math.round()
        }
     }
}

• javascript

Share Improve this question Follow edited Sep 30, 2022 at 20:13 isherwood 61.2k1616 gold badges121121 silver badges170170 bronze badges asked Jul 26, 2017 at 22:31 jSchmitzjSchmitz 111 silver badge11 bronze badge 2

• 4 What result were you expecting from calling Math.round with no arguments? – wbadart Commented Jul 26, 2017 at 22:34
• 5 Why would just throwing Math.round() in there with no arguments and without returning the result anywhere do anything at all? Maybe you should just read the docs for whatever method you're trying to use, and look at the examples. – adeneo Commented Jul 26, 2017 at 22:34

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 5

You can try one of these methods to do that according to your requirements:

• Math.floor()

  intvalue = Math.floor( floatvalue );

• Math.ceil()

  intvalue = Math.ceil( floatvalue );

• Math.round()

  intvalue = Math.round( floatvalue );

Example:

value = 3.65

Math.ceil(value); // 4

Math.floor(value); // 3

Math.round(value); // 4

in your function :

you should pass argument to method math.round to work as expected :

Math.round(r.items[k].inventory);

Math.round works just fine. Put the thing you want rounded in between the parentheses ().

let foo = {
  stat: "ok",
  items: {
    apple: {
      inventory: 18.45
    }
  }
}

function D(r) {
  if (r.stat === "ok") {
    for (var k in r.items) {
      console.log(Math.round(r.items[k].inventory))
    }
  }
}

D(foo);

Rounding numbers.

There are many ways to round a number each with slight differences.

To closest integer

Generally you round to the closest whole number

Math.round(9.4) == 9; // is true
Math.round(9.6) == 10; // is true

Math.round(-9.4) == -9; // is true
Math.round(-9.6) == -10; // is true

Midway point round up

In the case where you are halfway you round up towards Infinity

Math.round(9.5) == 10; // is true
Math.round(-9.5) == 9; // is true

You do not round to the nearest even

 Math.round(8.5) == 9; // is true
 Math.round(-7.5) == -7; // is true

Midway point round away from zero

If you want to round the mid point away from 0 you can use

 9.5.toFixed() == 10; // is true
-9.5.toFixed() == -10; // is true

Note the result is a string so if you want a number convert it as follows

Number( 9.5.toFixed()) === 10; // is true
Number(-9.5.toFixed()) === -10; // is true

Midway point round to even

If you wish to round to the nearest even you will have to create a function

const roundEven = (val) => {
    if (Math.abs(val % 1) === 0.5) {
        return (val = Math.round(val), val - (val % 2) * Math.sign(val));
    }
    return Math.round(val);
}


roundEven(9.5) === 10; // is true
roundEven(-9.5) === -10; // is true
roundEven(8.5) === 8; // is true
roundEven(-8.5) === -8; // is true

Example

show("Math.round(9.4) === " + Math.round(9.4))
show("Math.round(9.6) === " + Math.round(9.6))

show("Math.round(-9.4) === " + Math.round(-9.4))
show("Math.round(-9.6) === " + Math.round(-9.6))

show("Math.round(9.5) === " + Math.round(9.5) )
show("Math.round(-9.5) === " + Math.round(-9.5) )


show("Math.round(8.5) === " + Math.round(8.5) )
show("Math.round(-7.5) === " + Math.round(-7.5) )

show(" 9.5.toFixed() === '" + 9.5.toFixed() + "'" )
show("-9.5.toFixed() === '" + -9.5.toFixed() + "'" )
   
show("Number( 9.5.toFixed()) === " + Number(9.5.toFixed()))
show("Number(-9.5.toFixed()) === " + Number(-9.5.toFixed()))


const roundEven = (val) => {
if (Math.abs(val % 1) === 0.5) {
    return (val = Math.round(val), val - (val % 2) * Math.sign(val));
}
return Math.round(val);
}

show("roundEven(9.5) === " + roundEven(9.5))
show("roundEven(-9.5) === " + roundEven(-9.5))
show("roundEven(8.5) === " + roundEven(8.5))
show("roundEven(-8.5) === " + roundEven(-8.5))
show("roundEven(0.5) === " + roundEven(0.5))
show("roundEven(-0.5) === " + roundEven(-0.5))



function show(text){
   const d = document.createElement("div");
   d.textContent = text;
   document.body.appendChild(d);
}

本文标签： javascriptMathround not returning integers as expectedStack Overflow