# 如何在JavaScript中舍入数字？

2020/10/28 17:42 · javascript ·  · 0评论

• 192.168 => 192.20
• 192.11 => 192.20
• 192.21 => 192.30
• 192.26 => 192.30
• 192.20 => 192.20

``````/**
* @param num The number to round
* @param precision The number of decimal places to preserve
*/
function roundUp(num, precision) {
precision = Math.pow(10, precision)
return Math.ceil(num * precision) / precision
}

roundUp(192.168, 1) //=> 192.2
``````

``````// Arguments: number to round, number of decimal places
function roundNumber(rnum, rlength) {
var newnumber = Math.round(rnum * Math.pow(10, rlength)) / Math.pow(10, rlength);
return newnumber;
}
``````

``````alert(roundNumber(192.168,2));
``````

``````Math.round(price * 10)/10
``````

``````(Math.round(price * 10)/10).toFixed(2)
``````

``````var num = 192.16;

console.log(    Math.ceil(num * 10) / 10    );``````

OP预计有两件事：

A.向上取整至十分之一，

B。在百分数处显示零（货币的典型需求）。

``````//Arguments: number to round, number of decimal places.

function roundPrice(rnum, rlength) {
var newnumber = Math.ceil(rnum * Math.pow(10, rlength-1)) / Math.pow(10, rlength-1);
var toTenths = newnumber.toFixed(rlength);
}

``````

``````function roundNumber(rnum, rlength) {
var newnumber = Math.round(rnum * Math.pow(10, rlength)) / Math.pow(10, rlength);
return newnumber;
}

function ceilNumber(rnum, rlength) {
var newnumber = Math.ceil(rnum * Math.pow(10, rlength)) / Math.pow(10, rlength);
return newnumber;
}

``````

``````function roundIt(num, precision) {
var rounder = Math.pow(10, precision);
return (Math.round(num * rounder) / rounder).toFixed(precision)
};
``````

``````function limitDecimal(num,decimal){
return num.toString().substring(0, num.toString().indexOf('.')) + (num.toString().substr(num.toString().indexOf('.'), decimal+1));
}
``````

``````equals(roundUp(9.69545, 4), 9.6955);
equals(roundUp(37.760000000000005, 4), 37.76);
equals(roundUp(5.83333333, 4), 5.8333);
``````

``````// Closure
(function() {
/**
* Decimal adjustment of a number.
*
* @param {String}  type  The type of adjustment.
* @param {Number}  value The number.
* @param {Integer} exp   The exponent (the 10 logarithm of the adjustment base).
* @returns {Number} The adjusted value.
*/
// If the exp is undefined or zero...
if (typeof exp === 'undefined' || +exp === 0) {
return Math[type](value);
}
value = +value;
exp = +exp;
// If the value is not a number or the exp is not an integer...
if (isNaN(value) || !(typeof exp === 'number' && exp % 1 === 0)) {
return NaN;
}
// If the value is negative...
if (value < 0) {
}
// Shift
value = value.toString().split('e');
value = Math[type](+(value[0] + 'e' + (value[1] ? (+value[1] - exp) : -exp)));
// Shift back
value = value.toString().split('e');
return +(value[0] + 'e' + (value[1] ? (+value[1] + exp) : exp));
}

// Decimal round
if (!Math.round10) {
Math.round10 = function(value, exp) {
};
}
// Decimal floor
if (!Math.floor10) {
Math.floor10 = function(value, exp) {
};
}
// Decimal ceil
if (!Math.ceil10) {
Math.ceil10 = function(value, exp) {
};
}
})();

// Round
Math.round10(55.55, -1);   // 55.6
Math.round10(55.549, -1);  // 55.5
Math.round10(55, 1);       // 60
Math.round10(54.9, 1);     // 50
Math.round10(-55.55, -1);  // -55.5
Math.round10(-55.551, -1); // -55.6
Math.round10(-55, 1);      // -50
Math.round10(-55.1, 1);    // -60
Math.round10(1.005, -2);   // 1.01 -- compare this with Math.round(1.005*100)/100 above
Math.round10(-1.005, -2);  // -1.01
// Floor
Math.floor10(55.59, -1);   // 55.5
Math.floor10(59, 1);       // 50
Math.floor10(-55.51, -1);  // -55.6
Math.floor10(-51, 1);      // -60
// Ceil
Math.ceil10(55.51, -1);    // 55.6
Math.ceil10(51, 1);        // 60
Math.ceil10(-55.59, -1);   // -55.5
Math.ceil10(-59, 1);       // -50
``````

parseInt总是四舍五入.....

``console.log(parseInt(5.8)+1);``