# Math.floor()

`Math.floor()` 返回小于或等于一个给定数字的最大整数。

Note:  `Math.floor() === `向下取整

## 语法

``Math.floor(x) ``

`x`

## 示例

### 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.
*/
// 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) {
};
}
// 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
// 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

ECMAScript 1st Edition. Implemented in JavaScript 1.0 Standard Initial definition.
ECMAScript 5.1 (ECMA-262)
Math.floor
Standard
ECMAScript 2015 (6th Edition, ECMA-262)
Math.floor

Standard
ECMAScript Latest Draft (ECMA-262)
Math.floor
Draft

## 浏览器兼容性

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