Built-in JavaScript Objects

Math object (sample)
1. Math.max(a, b) - Returns the larger of the two values
```
let x = Math.max(4, Math.PI);  // 4  
```
2. Math.pow(a, b) - Returns a to the power of b
```
let x = Math.pow(2, 3);  // 8
```
3. Math.sqrt(n) - Returns the square root of n
```
let x = Math.sqrt(25);  // 5
```
4. Math.random() - Returns a pseudorandom number between 0.0 and 1.0
```
// Get a random number between 1 and 10 (inclusive)
let x = Math.floor(1 + Math.random() * 10);  
```
String object (sample)
1. charAt(i) - Returns the character at index i or an empty string if no character is present at that index
```
let s = "Hello there!";
let t = s.charAt(0);  // "H"
t = s[1];   // [] works the same, returns "e"
```
2. indexOf(s, [i]) - Returns the first occurence of the substring s starting at the position i, -1 if the substring is not found
```
let s = "Hello there!";
let t = s.indexOf("the");  // 6
```
3. replace(search, replace) - Replaces the first search string with the replace string and returns the modified string
```
let s = "Hello there!";
s = s.replace("there", "man");  // "Hello man!"  
```
4. substr(start, length) - Returns a substring with length length (optional) that begins at index start
```
let s = "Hello there!";
s = s.substr(6, 5);  // "there"
```
5. trim() - Returns a string with all white space at beginning and end removed
```
let s = "    Hello there!     ";
s = s.trim();  // "Hello there!"
```
6. split(delimiter) - Returns a an array that splits the string with the given delimiter
```
let s = "This is a test";
let words = s.split(" ");  // ["This", "is", "a", "test"]
```
7. Template literal is a string enclosed in `back-ticks` that allows expressions to be embedded
```
x = 4;
y = 3;
s = `${x} - ${y} = ${x - y}`;  // "4 - 3 = 1"
```

For obtaining and manipulating dates and times

let now = new Date();
s = now.toString();       // Tue Aug 21 2012 16:17:26 GMT-0500 (Central Daylight Time)
s = now.getDate();        // 21
s = now.getDay();         // 2 (0-6 for Sun-Sat)
s = now.getMonth();       // 7 (0-11 for Jan-Dec)
s = now.getFullYear();    // 2012
s = now.getTime();        // 1345584701802 (milliseconds since midnight Jan 1, 1970)
s = now.getHours();       // 16
s = now.getMinutes();     // 17
s = now.getSeconds();     // 26

Comparing dates/times

let billGates = new Date(1955, 9, 28);   // Oct 28, 1955  
let steveJobs = new Date(1955, 1, 24);   // Feb 24, 1955

let oneDay = 1000 * 60 * 60 * 24;    // Milliseconds in a day

// "Steve is older by 246 days."
if (billGates < steveJobs) {
	let diff = Math.ceil((steveJobs.getTime() - billGates.getTime()) / oneDay);
	document.writeln("Bill is older by " + diff + " days.");
}
else {
	let diff = Math.ceil((billGates.getTime() - steveJobs.getTime()) / oneDay);
	document.writeln("Steve is older by " + diff + " days.");
}