Create Docs “glossary/mathfloor/index”

src/pages/docs/glossary/mathfloor/index.md

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+---
+title: mathfloor
+template: docs
+excerpt: The Math.floor() function returns the largest integer less than or
+  equal to a given number.
+---
+# Math.floor()
+
+The `Math.floor()` function returns the largest integer less than or equal to a given number.
+
+## Syntax
+
+    Math.floor(x)
+
+### Parameters
+
+`x`  
+A number.
+
+### Return value
+
+A number representing the largest integer less than or equal to the specified number.
+
+## Description
+
+Because `floor()` is a static method of `Math`, you always use it as `Math.floor()`, rather than as a method of a `Math` object you created (`Math` is not a constructor).
+
+**Note:** `Math.floor(null)` returns 0, not a [`NaN`](../nan).
+
+## Examples
+
+### Using 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
+
+### Decimal adjustment
+
+```js
+
+
+
+    /**
+     * 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
+    const round10 = (value, exp) => decimalAdjust('round', value, exp);
+    // Decimal floor
+    const floor10 = (value, exp) => decimalAdjust('floor', value, exp);
+    // Decimal ceil
+    const ceil10 = (value, exp) => decimalAdjust('ceil', value, exp);
+
+    // Round
+    round10(55.55, -1);   // 55.6
+    round10(55.549, -1);  // 55.5
+    round10(55, 1);       // 60
+    round10(54.9, 1);     // 50
+    round10(-55.55, -1);  // -55.5
+    round10(-55.551, -1); // -55.6
+    round10(-55, 1);      // -50
+    round10(-55.1, 1);    // -60
+    // Floor
+    floor10(55.59, -1);   // 55.5
+    floor10(59, 1);       // 50
+    floor10(-55.51, -1);  // -55.6
+    floor10(-51, 1);      // -60
+    // Ceil
+    ceil10(55.51, -1);    // 55.6
+    ceil10(51, 1);        // 60
+    ceil10(-55.59, -1);   // -55.5
+    ceil10(-59, 1);       // -50
+
+```