Math.round()

// Returns the value 20 x = Math.round(20.49); // Returns the value 21 x = Math.round(20.5); // Returns the value -20 x = Math.round(-20.5); // Returns the value -21 x = Math.round(-20.51); // Returns the value 1 (!) // Note the rounding error because of inaccurate floating point arithmetics // Compare this with Math.round10(1.005, -2) from the example below x = Math.round(1.005 * 100) / 100;

// 閉包含數 (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. */ function decimalAdjust(type, value, exp) { // 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; } // 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) { return decimalAdjust("round", value, exp); }; } // Decimal floor if (!Math.floor10) { Math.floor10 = function (value, exp) { return decimalAdjust("floor", value, exp); }; } // Decimal ceil if (!Math.ceil10) { Math.ceil10 = function (value, exp) { return decimalAdjust("ceil", 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 // 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