JavaScript's Math Object
There is a large Math object pre-programmed into JavaScript. It has a lot of useful features that you can use in your coding. Some of the methods are straightforward. Others, I'll discuss a little more.
Getting an Integer (Rounding)
There are actually three ways to get an integer using the Math object.
Syntax:
- //moves up to the next whole number
- Math.ceil(number);
- //rounds up if the decimal is .5 or higher, else down
- Math.round(number);
- //moves down to the next whole number
- Math.floor(number);
Examples:
- Math.ceil(3.4); //4
- Math.ceil(3.6); //4
- Math.round(3.4); //3
- Math.round(3.6); //4
- Math.floor(3.4); //3
- Math.floor(3.6); //3
Note: Math.floor(); is used most often
because computers index from zero, such as with arrays.
Pi (π)
Very useful for anything involving circles, in particular. Use Math.PI; to return the value of π. Note: no parentheses here.
- Math.PI; //3.141592653589793
Absolute Value
Absolute value removes any negative sign from a number and gives you the positive value. No numbers are harmed during this process.
Syntax:
- Math.abs(number);
Examples:
- Math.abs(-34.6); //returns 34.6
- Math.abs(48); //returns 48
Exponential Powers
If you need to raise a number to an exponent, you need to use this method. Raising a number to a power means multiplying itself as many times as the exponent says to.
For example, 47 is 4 * 4 * 4 * 4 * 4 * 4 * 4 which equals 16384.
You can also use negative exponents, as in: 4-7 which is
1/47 or 1/4 * 1/4 *
1/4 * 1/4 * 1/4 * 1/4 *
1/4 or 1/16384 which is
0.00006103515625. Whew!
Use Math.pow(x, y); to compute x to the
power of y, or xy.
Examples:
- Math.pow(4, 7); //47 → 16384
- Math.pow(4, -7); //4-7 → 0.00006103515625
- Math.pow(-2, 10); //-210 → 1024
If you need a root of a number, like the cube root, you can put in a fractional (or decimal) exponent. Due to how JavaScript calculates numbers, you may not get a perfect answer. A cube root is a number to the one-third power. A square root is a number to the one-half power, and so on. What about a fourth root?
- Math.pow(4, 3); //four cubed: 43 = 64, so...
- Math.pow(64, (1/3)); //641/3 = 3.9999999999... → 4
- Math.pow(16, (1/4)); //161/4 = 2
JavaScript has a shortcut operator ** that does the same thing as Math.pow().
- 4 ** 7; //47 → 16384
Square Roots and Cube Roots
Although you can use the Math.pow(x,y); method to calculate a square or cube root, the Math object has special methods for square and cube roots.
For a square root, use Math.sqrt(number); This is the same as if you
used Math.pow(x, 0.5); or Math.pow(x, (1/2));
For a cube root, use Math.cbrt(number);.
Examples:
- Math.sqrt(9); //3
- Math.sqrt(Math.PI); //sqrt of π: 1.7724538509055159
- Math.cbrt(27); //3
Minimum/Maximum
If you pass in a set of numbers, this will return the minimum or maximum value, depending on which method you use.
- Math.min(number1, number2 , ...); //gets the minimum
- Math.max(number1, number2 , ...); //gets the maximum
Examples:
- Math.min(5, 73, -54, 0.032, 100); //-54
- Math.max(5, 73, -54, 0.032, 100); //100
Using Math.min() and Math.max() to keep numbers within a range
Sidenote: You
may not need this next part all that often. Usually you just need to stop a number from being too small (like hit
points going below 0) or too high (like only having up to 4 people playing Mario Kart in the living room at once).
These are very useful if you need to keep a number variable bound between within a range. Let's you need a number
from 2 to 18 and you have variable n that can change. Note that you use
Math.min(); to stop at the top of the range and Math.max(); to stop at the bottom.
- //This caps the number at 18
- n = Math.min(n, 18);
- //This floors the number at 2
- n = Math.max(n, 2);
- //This does both at the same time!
- n = Math.max(Math.min(n, 18), 2);
In generic form, where range is from low to high, you would use this.
- variable = Math.max(Math.min(variable, high), low);