This section I will be covering Objects in greater detail and the basic data types and finally working with primitives and primitive wrappers
Javascript provides a date type object and is based on the Java version, it stores dates from Jan 1 1970 using milliseconds pass this date, if you don't pass any arguments it will store the current date and time. There are many functions that you can use which I will detail below
| current date/time | let now = new Date(); |
| specific date/time | let someDate = new Date(2019, 0, 1);
let someDate = new Date("May 23, 2019");
let someDate = new Date(Date.UTC(2020, 4, 5, 17, 55, 55)); |
| get Specific elements of a date | let someDate = new Date("May 23, 2019");
console.log(someDate.toString());
console.log(someDate.getFullYear())
console.log(someDate.getMonth())
console.log(someDate.getDate())
console.log(someDate.getDay())
Note: there are many methods to extract specific date, month, date, day, hours, mintues, seconds, etc |
Regular expressions are used by many programming languages, it made up of 3 parts, th string to manipulate, the pattern and any flags
| Regexp flags |
|
| regexp instance properties | let pattern1 = /\[bc\]at/i;
console.log(pattern1.global); // false
console.log(pattern1.ignoreCase); // true
console.log(pattern1.multiline); // false
console.log(pattern1.lastIndex); // 0
console.log(pattern1.source); // "\[bc\]at"
console.log(pattern1.flags); // "i" |
| RegExp instance methods | let text = "mom and dad and baby"; let pattern = /mom( and dad( and baby)?)?/gi; let matches = pattern.exec(text); console.log(matches.index); // 0 console.log(matches.input); // "mom and dad and baby" console.log(matches[0]); // "mom and dad and baby" console.log(matches[1]); // " and dad and baby" console.log(matches[2]); // " and baby" |
| RegExp constructor properties | let text = "this has been a short summer";
let pattern = /(.)hort/g;
if (pattern.test(text)) {
console.log(RegExp.input); // this has been a short summer
console.log(RegExp.leftContext); // this has been a
console.log(RegExp.rightContext); // summer
console.log(RegExp.lastMatch); // short
console.log(RegExp.lastParen); // s
} |
| regular expression examples | let pattern1 = /at/g; // Match all instances of "at" in a string let pattern2 = /[bc]at/i; // Match the first instance of "bat" or "cat", regardless of case let pattern3 = /.at/gi; // Match all three-character combinations ending with "at", regardless of case |
I have also covered Regular Expressions in my Java and Python sections.
There are three special wrapper types in Javascript, Boolean, Number and String types, these Object types have methods that you can use to manipulate the data in the Object. There are many methods that you can use i list a few examples below
| Boolean Type | let trueObject = new Boolean(true); let falseObject = new Boolean(false); let result = falseObject && true; // true console.log(typeof falseObject); // object console.log(typeof falseValue); // boolean console.log(falseObject instanceof Boolean); // true console.log(falseValue instanceof Boolean); // false |
| Number Type | let numberObject = new Number(10); console.log(num.toString()); // "10" console.log(num.toString(2)); // "1010" console.log(num.toString(8)); // "12" console.log(num.toString(10)); // "10" console.log(num.toString(16)); // "a" console.log(num.toFixed(2)); // "10.00" console.log(num.toPrecision(3)); // "99.0" |
| String Type | let stringValue = new String("hello world");
console.log(stringValue.length); // "11"
console.log(stringValue.charAt(2)); // "c"
let result = stringValue.concat("world");
let result = stringValue.concat("world", "!");
let stringValue = "hello world";
console.log(stringValue.slice(3)); // "lo world"
console.log(stringValue.substring(3)); // "lo world"
console.log(stringValue.substr(3)); // "lo world"
console.log(stringValue.slice(3, 7)); // "lo w"
console.log(stringValue.substring(3,7)); // "lo w"
console.log(stringValue.substr(3, 7)); // "lo worl"
console.log(stringValue.slice(-3)); // "rld"
console.log(stringValue.substring(-3)); // "hello world"
console.log(stringValue.startsWith("foo")); // true
console.log(stringValue.startsWith("bar")); // false
console.log(stringValue.endsWith("baz")); // true
console.log(stringValue.endsWith("bar")); // false
console.log(stringValue.includes("bar")); // true
console.log(stringValue.includes("qux")); // false
console.log(stringValue.toLocaleUpperCase()); // "HELLO WORLD"
console.log(stringValue.toUpperCase()); // "HELLO WORLD"
|
There are two singleton built-in Objects Global and Math, The Global object is not explicity accessible, its a catch all object for properties and methods that don't have an object, this is were all global variables reside, it also has many functions like isNaN(), parseInt(), etc, the Global object also has many properties such as Object, Array Function, etc all of which are constructors for creating Objects. There are many more here are a few wexamples which I want to make you aware of
| Global Object methods | let uri = "http:// www.wrox.com/illegal value.js#start";
console.log(encodeURI(uri));
et uri = "http%3A%2F%2Fwww.wrox.com%2Fillegal%20value.js%23start";
console.log(decodeURI(uri));
let msg = "hello world";
eval("console.log(msg)"); // "hello world"
Note: The eval() function evaluates or executes an argument. |
The Math object provides mathematical formulas, information and computation. The object has a number of properties like PI, SQRT2, etc and many methods like max(), min(), ceil(), floor(), random(), etc.
| MATH object properties and functions | let pi = Math.PI
let max = Math.max(3, 54, 32, 16);
let min = Math.min(3, 54, 32, 16);
console.log(Math.ceil(25.9)); // 26
console.log(Math.ceil(25.5)); // 26
console.log(Math.ceil(25.1)); // 26
console.log(Math.round(25.9)); // 26
console.log(Math.round(25.5)); // 26
console.log(Math.round(25.1)); // 25
console.log(Math.floor(25.9)); // 25
console.log(Math.floor(25.5)); // 25
console.log(Math.floor(25.1)); // 25
number = Math.floor(Math.random() * 10 + 1) // 10 = choices and 1 = lowver value |