From 33058f2b292b3a581333bdfb21b8f671898c5060 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:40:17 -0500 Subject: initial commit --- .../reference/global_objects/math/floor/index.html | 222 +++++++++++++++++++++ 1 file changed, 222 insertions(+) create mode 100644 files/zh-cn/web/javascript/reference/global_objects/math/floor/index.html (limited to 'files/zh-cn/web/javascript/reference/global_objects/math/floor') diff --git a/files/zh-cn/web/javascript/reference/global_objects/math/floor/index.html b/files/zh-cn/web/javascript/reference/global_objects/math/floor/index.html new file mode 100644 index 0000000000..f41d9aedfc --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/math/floor/index.html @@ -0,0 +1,222 @@ +--- +title: Math.floor() +slug: Web/JavaScript/Reference/Global_Objects/Math/floor +tags: + - Math.floor() + - 向下取整 +translation_of: Web/JavaScript/Reference/Global_Objects/Math/floor +--- +
{{JSRef}}
+ 
+ +

Math.floor() 返回小于或等于一个给定数字的最大整数。

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+

Note:  可以理解 Math.floor()为向下取整

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+ +

语法

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Math.floor(x)
+ +

参数

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+
x
+
一个数字。
+
+

返回值 

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一个表示小于或等于指定数字的最大整数的数字。

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+
+ +

描述

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由于 floor 是 Math 的一个静态方法，你总是应该像这样使用它 Math.floor()，而不是作为你创建的一个Math对象的一种方法（Math不是一个构造函数）。

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示例

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例子：使用 Math.floor

+ +
Math.floor( 45.95);
+// 45
+Math.floor( 45.05);
+// 45
+Math.floor( 4 );
+// 4
+Math.floor(-45.05);
+// -46
+Math.floor(-45.95);
+// -46
+
+
+ +

例子：十进制调整

+ +
// 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.
+	 */
+	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
+// 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
+
+ +

规范

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规范版本规范状态注解
ECMAScript 1st Edition. Implemented in JavaScript 1.0StandardInitial definition.
{{SpecName('ES5.1', '#sec-15.8.2.9', 'Math.floor')}}{{Spec2('ES5.1')}}
{{SpecName('ES6', '#sec-math.floor', 'Math.floor')}} {{Spec2('ES6')}}
{{SpecName('ESDraft', '#sec-math.floor', 'Math.floor')}}{{Spec2('ESDraft')}}
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浏览器兼容性

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{{ CompatibilityTable() }}

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FeatureChromeFirefox (Gecko)Internet ExplorerOperaSafari
Basic support{{ CompatVersionUnknown() }}{{ CompatVersionUnknown() }}{{ CompatVersionUnknown() }}{{ CompatVersionUnknown() }}{{ CompatVersionUnknown() }}
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+ + + + + + + + + + + + + + + + + + + + + +
FeatureAndroidChrome for AndroidFirefox Mobile (Gecko)IE MobileOpera MobileSafari Mobile
Basic support{{ CompatVersionUnknown() }}{{ CompatVersionUnknown() }}{{ CompatVersionUnknown() }}{{ CompatVersionUnknown() }}{{ CompatVersionUnknown() }}{{ CompatVersionUnknown() }}
+
+ +

相关链接

+ + -- cgit v1.2.3-54-g00ecf