如何在JavaScript中四舍五入一个数字?
Math.round()不起作用，因为它舍入到最接近的小数。
我不确定是否有更好的方法，而不是在小数点处分开，保留第一位。一定有……
当前回答
朝向负无穷- Math.floor()
+3.5 => +3.0
-3.5 => -4.0
可以使用Math.trunc()向零舍入。旧的浏览器不支持此功能。如果需要支持这些，可以使用Math.ceil()表示负数，使用Math.floor()表示正数。
+3.5 => +3.0 using Math.floor()
-3.5 => -3.0 using Math.ceil()
其他回答
如果需要四舍五入到特定的小数点后数位，可以尝试使用此函数
function roundDown(number, decimals) {
decimals = decimals || 0;
return ( Math.floor( number * Math.pow(10, decimals) ) / Math.pow(10, decimals) );
}
例子
alert(roundDown(999.999999)); // 999
alert(roundDown(999.999999, 3)); // 999.999
alert(roundDown(999.999999, -1)); // 990
Math.floor()可以工作，但与使用按位或操作相比，它非常慢:
var rounded = 34.923 | 0;
alert( rounded );
//alerts "34"
EDIT Math.floor()并不比使用|操作符慢。感谢Jason S检查我的工作。
下面是我用来测试的代码:
var a = [];
var time = new Date().getTime();
for( i = 0; i < 100000; i++ ) {
//a.push( Math.random() * 100000 | 0 );
a.push( Math.floor( Math.random() * 100000 ) );
}
var elapsed = new Date().getTime() - time;
alert( "elapsed time: " + elapsed );
Math.floor(1+7/8)
这是数学。在一个简单的例子中使用地板。这可能会帮助新开发人员了解如何在函数中使用它以及它的功能。希望能有所帮助!
<script>
var marks = 0;
function getRandomNumbers(){ // generate a random number between 1 & 10
var number = Math.floor((Math.random() * 10) + 1);
return number;
}
function getNew(){
/*
This function can create a new problem by generating two random numbers. When the page is loading as the first time, this function is executed with the onload event and the onclick event of "new" button.
*/
document.getElementById("ans").focus();
var num1 = getRandomNumbers();
var num2 = getRandomNumbers();
document.getElementById("num1").value = num1;
document.getElementById("num2").value = num2;
document.getElementById("ans").value ="";
document.getElementById("resultBox").style.backgroundColor = "maroon"
document.getElementById("resultBox").innerHTML = "***"
}
function checkAns(){
/*
After entering the answer, the entered answer will be compared with the correct answer.
If the answer is correct, the text of the result box should be "Correct" with a green background and 10 marks should be added to the total marks.
If the answer is incorrect, the text of the result box should be "Incorrect" with a red background and 3 marks should be deducted from the total.
The updated total marks should be always displayed at the total marks box.
*/
var num1 = eval(document.getElementById("num1").value);
var num2 = eval(document.getElementById("num2").value);
var answer = eval(document.getElementById("ans").value);
if(answer==(num1+num2)){
marks = marks + 10;
document.getElementById("resultBox").innerHTML = "Correct";
document.getElementById("resultBox").style.backgroundColor = "green";
document.getElementById("totalMarks").innerHTML= "Total marks : " + marks;
}
else{
marks = marks - 3;
document.getElementById("resultBox").innerHTML = "Wrong";
document.getElementById("resultBox").style.backgroundColor = "red";
document.getElementById("totalMarks").innerHTML = "Total Marks: " + marks ;
}
}
</script>
</head>
<body onLoad="getNew()">
<div class="container">
<h1>Let's add numbers</h1>
<div class="sum">
<input id="num1" type="text" readonly> + <input id="num2" type="text" readonly>
</div>
<h2>Enter the answer below and click 'Check'</h2>
<div class="answer">
<input id="ans" type="text" value="">
</div>
<input id="btnchk" onClick="checkAns()" type="button" value="Check" >
<div id="resultBox">***</div>
<input id="btnnew" onClick="getNew()" type="button" value="New">
<div id="totalMarks">Total marks : 0</div>
</div>
</body>
</html>
这是我发现的最可靠的解决方案。
function round(value, decimals) {
return Number(Math.floor(parseFloat(value + 'e' + decimals)) + 'e-' + decimals);
}
来源:Jack L Moore的博客
